FAILED: patch "[PATCH] signal: Don't always set SA_IMMUTABLE for forced signals" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From e349d945fac76bddc78ae1cb92a0145b427a87ce Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Thu, 18 Nov 2021 11:11:13 -0600
Subject: [PATCH] signal: Don't always set SA_IMMUTABLE for forced signals

Recently to prevent issues with SECCOMP_RET_KILL and similar signals being changed before they are delivered SA_IMMUTABLE was added.

Unfortunately this broke debuggers[1][2] which reasonably expect to be able to trap synchronous SIGTRAP and SIGSEGV even when the target process is not configured to handle those signals.

Update force_sig_to_task to support both the case when we can allow the debugger to intercept and possibly ignore the signal and the case when it is not safe to let userspace know about the signal until the process has exited.

Suggested-by Linus Torvalds <[email protected]>

Reported-by Kyle Huey <[email protected]>

Reported-by kernel test robot <[email protected]>

Cc [email protected]

[1] https://lkml.kernel.org/r/CAP045AoMY4xf8aC_4QU_-j7obuEPYgTcnQQP3Yxk=2X90jtpjw@mail.gmail.com
[2] https://lkml.kernel.org/r/20211117150258.GB5403@xsang-OptiPlex-9020

Fixes 00b06da29cf9 ("signal: Add SA_IMMUTABLE to ensure forced siganls do not get changed")

Link https://lkml.kernel.org/r/[email protected] open here

Reviewed-by Kees Cook <[email protected]>

Tested-by Kees Cook <[email protected]>

Tested-by Kyle Huey <[email protected]>

Signed-off-by "Eric W. Biederman" <[email protected]>

kernel/signal.c +16 -7

index 7c4b7ae714d4..7815e1bbeddc 100644
@@ -1298,6 +1298,12 @@ int do_send_sig_info(int sig, struct kernel_siginfo *info, struct task_struct *p
        return ret;
 }
 
+enum sig_handler {
+       HANDLER_CURRENT, /* If reachable use the current handler */
+       HANDLER_SIG_DFL, /* Always use SIG_DFL handler semantics */
+       HANDLER_EXIT,    /* Only visible as the process exit code */
+};
+
 /*
  * Force a signal that the process can't ignore: if necessary
  * we unblock the signal and change any SIG_IGN to SIG_DFL.

@@ -1310,7 +1316,8 @@ int do_send_sig_info(int sig, struct kernel_siginfo *info, struct task_struct *p
  * that is why we also clear SIGNAL_UNKILLABLE.
  */
 static int
-force_sig_info_to_task(struct kernel_siginfo *info, struct task_struct *t, bool sigdfl)
+force_sig_info_to_task(struct kernel_siginfo *info, struct task_struct *t,
+       enum sig_handler handler)
 {
        unsigned long int flags;
        int ret, blocked, ignored;

@@ -1321,9 +1328,10 @@ force_sig_info_to_task(struct kernel_siginfo *info, struct task_struct *t, bool
        action = &t->sighand->action[sig-1];
        ignored = action->sa.sa_handler == SIG_IGN;
        blocked = sigismember(&t->blocked, sig);
-       if (blocked || ignored || sigdfl) {
+       if (blocked || ignored || (handler != HANDLER_CURRENT)) {
                action->sa.sa_handler = SIG_DFL;
-               action->sa.sa_flags |= SA_IMMUTABLE;
+               if (handler == HANDLER_EXIT)
+                       action->sa.sa_flags |= SA_IMMUTABLE;
                if (blocked) {
                        sigdelset(&t->blocked, sig);
                        recalc_sigpending_and_wake(t);

@@ -1343,7 +1351,7 @@ force_sig_info_to_task(struct kernel_siginfo *info, struct task_struct *t, bool
 
 int force_sig_info(struct kernel_siginfo *info)
 {
-       return force_sig_info_to_task(info, current, false);
+       return force_sig_info_to_task(info, current, HANDLER_CURRENT);
 }
 
 /*

@@ -1660,7 +1668,7 @@ void force_fatal_sig(int sig)
        info.si_code = SI_KERNEL;
        info.si_pid = 0;
        info.si_uid = 0;
-       force_sig_info_to_task(&info, current, true);
+       force_sig_info_to_task(&info, current, HANDLER_SIG_DFL);
 }
 
 /*

@@ -1693,7 +1701,7 @@ int force_sig_fault_to_task(int sig, int code, void __user *addr
        info.si_flags = flags;
        info.si_isr = isr;
 #endif
-       return force_sig_info_to_task(&info, t, false);
+       return force_sig_info_to_task(&info, t, HANDLER_CURRENT);
 }
 
 int force_sig_fault(int sig, int code, void __user *addr

@@ -1813,7 +1821,8 @@ int force_sig_seccomp(int syscall, int reason, bool force_coredump)
        info.si_errno = reason;
        info.si_arch = syscall_get_arch(current);
        info.si_syscall = syscall;
-       return force_sig_info_to_task(&info, current, force_coredump);
+       return force_sig_info_to_task(&info, current,
+               force_coredump ? HANDLER_EXIT : HANDLER_CURRENT);
 }
 
 /* For the crazy architectures that include trap information in

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From e349d945fac76bddc78ae1cb92a0145b427a87ce Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Thu, 18 Nov 2021 11:11:13 -0600
Subject: [PATCH] signal: Don't always set SA_IMMUTABLE for forced signals

Recently to prevent issues with SECCOMP_RET_KILL and similar signals being changed before they are delivered SA_IMMUTABLE was added.

Unfortunately this broke debuggers[1][2] which reasonably expect to be able to trap synchronous SIGTRAP and SIGSEGV even when the target process is not configured to handle those signals.

Update force_sig_to_task to support both the case when we can allow the debugger to intercept and possibly ignore the signal and the case when it is not safe to let userspace know about the signal until the process has exited.

Suggested-by Linus Torvalds <[email protected]>

Reported-by Kyle Huey <[email protected]>

Reported-by kernel test robot <[email protected]>

Cc [email protected]

[1] https://lkml.kernel.org/r/CAP045AoMY4xf8aC_4QU_-j7obuEPYgTcnQQP3Yxk=2X90jtpjw@mail.gmail.com
[2] https://lkml.kernel.org/r/20211117150258.GB5403@xsang-OptiPlex-9020

Fixes 00b06da29cf9 ("signal: Add SA_IMMUTABLE to ensure forced siganls do not get changed")

Link https://lkml.kernel.org/r/[email protected] open here

Reviewed-by Kees Cook <[email protected]>

Tested-by Kees Cook <[email protected]>

Tested-by Kyle Huey <[email protected]>

Signed-off-by "Eric W. Biederman" <[email protected]>

kernel/signal.c +16 -7

index 7c4b7ae714d4..7815e1bbeddc 100644
@@ -1298,6 +1298,12 @@ int do_send_sig_info(int sig, struct kernel_siginfo *info, struct task_struct *p
  	return ret;
  }
 
+enum sig_handler {
+	HANDLER_CURRENT, /* If reachable use the current handler */
+	HANDLER_SIG_DFL, /* Always use SIG_DFL handler semantics */
+	HANDLER_EXIT,	 /* Only visible as the process exit code */
+};
+
  /*
   * Force a signal that the process can't ignore: if necessary
   * we unblock the signal and change any SIG_IGN to SIG_DFL.

@@ -1310,7 +1316,8 @@ int do_send_sig_info(int sig, struct kernel_siginfo *info, struct task_struct *p
   * that is why we also clear SIGNAL_UNKILLABLE.
   */
  static int
-force_sig_info_to_task(struct kernel_siginfo *info, struct task_struct *t, bool sigdfl)
+force_sig_info_to_task(struct kernel_siginfo *info, struct task_struct *t,
+	enum sig_handler handler)
  {
  	unsigned long int flags;
  	int ret, blocked, ignored;

@@ -1321,9 +1328,10 @@ force_sig_info_to_task(struct kernel_siginfo *info, struct task_struct *t, bool
  	action = &t->sighand->action[sig-1];
  	ignored = action->sa.sa_handler == SIG_IGN;
  	blocked = sigismember(&t->blocked, sig);
-	if (blocked || ignored || sigdfl) {
+	if (blocked || ignored || (handler != HANDLER_CURRENT)) {
  		action->sa.sa_handler = SIG_DFL;
-		action->sa.sa_flags |= SA_IMMUTABLE;
+		if (handler == HANDLER_EXIT)
+			action->sa.sa_flags |= SA_IMMUTABLE;
  		if (blocked) {
  			sigdelset(&t->blocked, sig);
  			recalc_sigpending_and_wake(t);

@@ -1343,7 +1351,7 @@ force_sig_info_to_task(struct kernel_siginfo *info, struct task_struct *t, bool
 
  int force_sig_info(struct kernel_siginfo *info)
  {
-	return force_sig_info_to_task(info, current, false);
+	return force_sig_info_to_task(info, current, HANDLER_CURRENT);
  }
 
  /*

@@ -1660,7 +1668,7 @@ void force_fatal_sig(int sig)
  	info.si_code = SI_KERNEL;
  	info.si_pid = 0;
  	info.si_uid = 0;
-	force_sig_info_to_task(&info, current, true);
+	force_sig_info_to_task(&info, current, HANDLER_SIG_DFL);
  }
 
  /*

@@ -1693,7 +1701,7 @@ int force_sig_fault_to_task(int sig, int code, void __user *addr
  	info.si_flags = flags;
  	info.si_isr = isr;
  #endif
-	return force_sig_info_to_task(&info, t, false);
+	return force_sig_info_to_task(&info, t, HANDLER_CURRENT);
  }
 
  int force_sig_fault(int sig, int code, void __user *addr

@@ -1813,7 +1821,8 @@ int force_sig_seccomp(int syscall, int reason, bool force_coredump)
  	info.si_errno = reason;
  	info.si_arch = syscall_get_arch(current);
  	info.si_syscall = syscall;
-	return force_sig_info_to_task(&info, current, force_coredump);
+	return force_sig_info_to_task(&info, current,
+		force_coredump ? HANDLER_EXIT : HANDLER_CURRENT);
  }
 
  /* For the crazy architectures that include trap information in

Den 2021-11-22 kl. 14:31, skrev [email protected]:

Quoted 9 lines

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

It will apply if you add this one first:

From 26d5badbccddcc063dc5174a2baffd13a23322aa Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:43:59 -0500
Subject: [PATCH] signal: Implement force_fatal_sig

and if the other patch for signal that has similar description should land in 5.15:

From fcb116bc43c8c37c052530ead79872f8b2615711 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Thu, 18 Nov 2021 14:23:21 -0600
Subject: [PATCH] signal: Replace force_fatal_sig with force_exit_sig when in doubt

then the list is looks something like:

From 941edc5bf174b67f94db19817cbeab0a93e0c32a Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:44:00 -0500
Subject: [PATCH] exit/syscall_user_dispatch: Send ordinary signals on failure

From 83a1f27ad773b1d8f0460d3a676114c7651918cc Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:43:53 -0500
Subject: [PATCH] signal/powerpc: On swapcontext failure force SIGSEGV

From 9bc508cf0791c8e5a37696de1a046d746fcbd9d8 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:43:57 -0500
Subject: [PATCH] signal/s390: Use force_sigsegv in default_trap_handler

From c317d306d55079525c9610267fdaf3a8a6d2f08b Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:44:01 -0500
Subject: [PATCH] signal/sparc32: Exit with a fatal signal when
try_to_clear_window_buffer fails

From 086ec444f86660e103de8945d0dcae9b67132ac9 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:44:02 -0500
Subject: [PATCH] signal/sparc32: In setup_rt_frame and setup_fram use
force_fatal_sig

From 1fbd60df8a852d9c55de8cd3621899cf4c72a5b7 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:43:56 -0500
Subject: [PATCH] signal/vm86_32: Properly send SIGSEGV when the vm86 state cannot be saved.

From 695dd0d634df8903e5ead8aa08d326f63b23368a Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:44:03 -0500
Subject: [PATCH] signal/x86: In emulate_vsyscall force a signal instead of calling do_exit

From 26d5badbccddcc063dc5174a2baffd13a23322aa Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:43:59 -0500
Subject: [PATCH] signal: Implement force_fatal_sig

From e21294a7aaae32c5d7154b187113a04db5852e37 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Mon, 25 Oct 2021 10:50:57 -0500
Subject: [PATCH] signal: Replace force_sigsegv(SIGSEGV) with
force_fatal_sig(SIGSEGV)

From e349d945fac76bddc78ae1cb92a0145b427a87ce Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Thu, 18 Nov 2021 11:11:13 -0600
Subject: [PATCH] signal: Don't always set SA_IMMUTABLE for forced signals

From fcb116bc43c8c37c052530ead79872f8b2615711 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Thu, 18 Nov 2021 14:23:21 -0600
Subject: [PATCH] signal: Replace force_fatal_sig with force_exit_sig when in doubt

Applying them in listed order on top of 5.14.4 and builds/runs on i586, x86_64, armv7hl, aarch64

Quoted 100 lines · Thomas Backlund

Den 2021-11-22 kl. 14:31, skrev [email protected]:

Quoted 9 lines

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

It will apply if you add this one first:

From 26d5badbccddcc063dc5174a2baffd13a23322aa Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:43:59 -0500
Subject: [PATCH] signal: Implement force_fatal_sig

and if the other patch for signal that has similar description should land in 5.15:

From fcb116bc43c8c37c052530ead79872f8b2615711 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Thu, 18 Nov 2021 14:23:21 -0600
Subject: [PATCH] signal: Replace force_fatal_sig with force_exit_sig when in doubt

then the list is looks something like:

From 941edc5bf174b67f94db19817cbeab0a93e0c32a Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:44:00 -0500
Subject: [PATCH] exit/syscall_user_dispatch: Send ordinary signals on failure

From 83a1f27ad773b1d8f0460d3a676114c7651918cc Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:43:53 -0500
Subject: [PATCH] signal/powerpc: On swapcontext failure force SIGSEGV

From 9bc508cf0791c8e5a37696de1a046d746fcbd9d8 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:43:57 -0500
Subject: [PATCH] signal/s390: Use force_sigsegv in default_trap_handler

From c317d306d55079525c9610267fdaf3a8a6d2f08b Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:44:01 -0500
Subject: [PATCH] signal/sparc32: Exit with a fatal signal when
try_to_clear_window_buffer fails

From 086ec444f86660e103de8945d0dcae9b67132ac9 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:44:02 -0500
Subject: [PATCH] signal/sparc32: In setup_rt_frame and setup_fram use
force_fatal_sig

From 1fbd60df8a852d9c55de8cd3621899cf4c72a5b7 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:43:56 -0500
Subject: [PATCH] signal/vm86_32: Properly send SIGSEGV when the vm86 state cannot be saved.

From 695dd0d634df8903e5ead8aa08d326f63b23368a Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:44:03 -0500
Subject: [PATCH] signal/x86: In emulate_vsyscall force a signal instead of calling do_exit

From 26d5badbccddcc063dc5174a2baffd13a23322aa Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:43:59 -0500
Subject: [PATCH] signal: Implement force_fatal_sig

From e21294a7aaae32c5d7154b187113a04db5852e37 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Mon, 25 Oct 2021 10:50:57 -0500
Subject: [PATCH] signal: Replace force_sigsegv(SIGSEGV) with
force_fatal_sig(SIGSEGV)

From e349d945fac76bddc78ae1cb92a0145b427a87ce Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Thu, 18 Nov 2021 11:11:13 -0600
Subject: [PATCH] signal: Don't always set SA_IMMUTABLE for forced signals

From fcb116bc43c8c37c052530ead79872f8b2615711 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Thu, 18 Nov 2021 14:23:21 -0600
Subject: [PATCH] signal: Replace force_fatal_sig with force_exit_sig when in doubt

Quoted 2 lines

Applying them in listed order on top of 5.14.4 and builds/runs on i586, x86_64, armv7hl, aarch64

That series list is crazy, let me go try it and see what blows up! :)

Quoted 104 lines · Greg KH

Quoted 102 lines · Thomas Backlund

Den 2021-11-22 kl. 14:31, skrev [email protected]:

Quoted 9 lines

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

It will apply if you add this one first:

From 26d5badbccddcc063dc5174a2baffd13a23322aa Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:43:59 -0500
Subject: [PATCH] signal: Implement force_fatal_sig

and if the other patch for signal that has similar description should land in 5.15:

From fcb116bc43c8c37c052530ead79872f8b2615711 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Thu, 18 Nov 2021 14:23:21 -0600
Subject: [PATCH] signal: Replace force_fatal_sig with force_exit_sig when in doubt

then the list is looks something like:

From 941edc5bf174b67f94db19817cbeab0a93e0c32a Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:44:00 -0500
Subject: [PATCH] exit/syscall_user_dispatch: Send ordinary signals on failure

From 83a1f27ad773b1d8f0460d3a676114c7651918cc Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:43:53 -0500
Subject: [PATCH] signal/powerpc: On swapcontext failure force SIGSEGV

From 9bc508cf0791c8e5a37696de1a046d746fcbd9d8 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:43:57 -0500
Subject: [PATCH] signal/s390: Use force_sigsegv in default_trap_handler

From c317d306d55079525c9610267fdaf3a8a6d2f08b Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:44:01 -0500
Subject: [PATCH] signal/sparc32: Exit with a fatal signal when
try_to_clear_window_buffer fails

From 086ec444f86660e103de8945d0dcae9b67132ac9 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:44:02 -0500
Subject: [PATCH] signal/sparc32: In setup_rt_frame and setup_fram use
force_fatal_sig

From 1fbd60df8a852d9c55de8cd3621899cf4c72a5b7 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:43:56 -0500
Subject: [PATCH] signal/vm86_32: Properly send SIGSEGV when the vm86 state cannot be saved.

From 695dd0d634df8903e5ead8aa08d326f63b23368a Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:44:03 -0500
Subject: [PATCH] signal/x86: In emulate_vsyscall force a signal instead of calling do_exit

From 26d5badbccddcc063dc5174a2baffd13a23322aa Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:43:59 -0500
Subject: [PATCH] signal: Implement force_fatal_sig

From e21294a7aaae32c5d7154b187113a04db5852e37 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Mon, 25 Oct 2021 10:50:57 -0500
Subject: [PATCH] signal: Replace force_sigsegv(SIGSEGV) with
force_fatal_sig(SIGSEGV)

From e349d945fac76bddc78ae1cb92a0145b427a87ce Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Thu, 18 Nov 2021 11:11:13 -0600
Subject: [PATCH] signal: Don't always set SA_IMMUTABLE for forced signals

From fcb116bc43c8c37c052530ead79872f8b2615711 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Thu, 18 Nov 2021 14:23:21 -0600
Subject: [PATCH] signal: Replace force_fatal_sig with force_exit_sig when in doubt

Applying them in listed order on top of 5.14.4 and builds/runs on i586, x86_64, armv7hl, aarch64

Quoted 1 line

That series list is crazy, let me go try it and see what blows up! :)

Maybe I am wrong but I think "Don't always set SA_IMMUTABLE for forced signals" will apply if you drop the hunk modifying force_fatal_sig. Then you don't need to backport all of the cleanups just the fix.

I will take a quick look and verify that.

Quoted 99 lines · Greg KH

Quoted 98 lines · Thomas Backlund

Den 2021-11-22 kl. 14:31, skrev [email protected]:

Quoted 8 lines

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

It will apply if you add this one first:

From 26d5badbccddcc063dc5174a2baffd13a23322aa Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:43:59 -0500
Subject: [PATCH] signal: Implement force_fatal_sig

and if the other patch for signal that has similar description should land in 5.15:

From fcb116bc43c8c37c052530ead79872f8b2615711 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Thu, 18 Nov 2021 14:23:21 -0600
Subject: [PATCH] signal: Replace force_fatal_sig with force_exit_sig when in doubt

then the list is looks something like:

From 941edc5bf174b67f94db19817cbeab0a93e0c32a Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:44:00 -0500
Subject: [PATCH] exit/syscall_user_dispatch: Send ordinary signals on failure

From 83a1f27ad773b1d8f0460d3a676114c7651918cc Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:43:53 -0500
Subject: [PATCH] signal/powerpc: On swapcontext failure force SIGSEGV

From 9bc508cf0791c8e5a37696de1a046d746fcbd9d8 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:43:57 -0500
Subject: [PATCH] signal/s390: Use force_sigsegv in default_trap_handler

From c317d306d55079525c9610267fdaf3a8a6d2f08b Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:44:01 -0500
Subject: [PATCH] signal/sparc32: Exit with a fatal signal when
try_to_clear_window_buffer fails

From 086ec444f86660e103de8945d0dcae9b67132ac9 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:44:02 -0500
Subject: [PATCH] signal/sparc32: In setup_rt_frame and setup_fram use
force_fatal_sig

From 1fbd60df8a852d9c55de8cd3621899cf4c72a5b7 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:43:56 -0500
Subject: [PATCH] signal/vm86_32: Properly send SIGSEGV when the vm86 state cannot be saved.

From 695dd0d634df8903e5ead8aa08d326f63b23368a Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:44:03 -0500
Subject: [PATCH] signal/x86: In emulate_vsyscall force a signal instead of calling do_exit

From 26d5badbccddcc063dc5174a2baffd13a23322aa Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:43:59 -0500
Subject: [PATCH] signal: Implement force_fatal_sig

From e21294a7aaae32c5d7154b187113a04db5852e37 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Mon, 25 Oct 2021 10:50:57 -0500
Subject: [PATCH] signal: Replace force_sigsegv(SIGSEGV) with
force_fatal_sig(SIGSEGV)

From e349d945fac76bddc78ae1cb92a0145b427a87ce Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Thu, 18 Nov 2021 11:11:13 -0600
Subject: [PATCH] signal: Don't always set SA_IMMUTABLE for forced signals

From fcb116bc43c8c37c052530ead79872f8b2615711 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Thu, 18 Nov 2021 14:23:21 -0600
Subject: [PATCH] signal: Replace force_fatal_sig with force_exit_sig when in doubt

Quoted 3 lines

Quoted 2 lines

Applying them in listed order on top of 5.14.4 and builds/runs on i586, x86_64, armv7hl, aarch64

That series list is crazy, let me go try it and see what blows up! :)

Maybe I am wrong but I think "Don't always set SA_IMMUTABLE for forced signals" will apply if you drop the hunk modifying force_fatal_sig. Then you don't need to backport all of the cleanups just the fix.

I will take a quick look and verify that.

Den 2021-11-23 kl. 21:24, skrev [email protected]:

Quoted 108 lines

Quoted 99 lines · Greg KH

Quoted 98 lines · Thomas Backlund

Den 2021-11-22 kl. 14:31, skrev [email protected]:

Quoted 8 lines

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

It will apply if you add this one first:

From 26d5badbccddcc063dc5174a2baffd13a23322aa Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:43:59 -0500
Subject: [PATCH] signal: Implement force_fatal_sig

and if the other patch for signal that has similar description should land in 5.15:

From fcb116bc43c8c37c052530ead79872f8b2615711 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Thu, 18 Nov 2021 14:23:21 -0600
Subject: [PATCH] signal: Replace force_fatal_sig with force_exit_sig when in doubt

then the list is looks something like:

From 941edc5bf174b67f94db19817cbeab0a93e0c32a Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:44:00 -0500
Subject: [PATCH] exit/syscall_user_dispatch: Send ordinary signals on failure

From 83a1f27ad773b1d8f0460d3a676114c7651918cc Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:43:53 -0500
Subject: [PATCH] signal/powerpc: On swapcontext failure force SIGSEGV

From 9bc508cf0791c8e5a37696de1a046d746fcbd9d8 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:43:57 -0500
Subject: [PATCH] signal/s390: Use force_sigsegv in default_trap_handler

From c317d306d55079525c9610267fdaf3a8a6d2f08b Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:44:01 -0500
Subject: [PATCH] signal/sparc32: Exit with a fatal signal when
try_to_clear_window_buffer fails

From 086ec444f86660e103de8945d0dcae9b67132ac9 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:44:02 -0500
Subject: [PATCH] signal/sparc32: In setup_rt_frame and setup_fram use
force_fatal_sig

From 1fbd60df8a852d9c55de8cd3621899cf4c72a5b7 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:43:56 -0500
Subject: [PATCH] signal/vm86_32: Properly send SIGSEGV when the vm86 state cannot be saved.

From 695dd0d634df8903e5ead8aa08d326f63b23368a Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:44:03 -0500
Subject: [PATCH] signal/x86: In emulate_vsyscall force a signal instead of calling do_exit

From 26d5badbccddcc063dc5174a2baffd13a23322aa Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Wed, 20 Oct 2021 12:43:59 -0500
Subject: [PATCH] signal: Implement force_fatal_sig

From e21294a7aaae32c5d7154b187113a04db5852e37 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Mon, 25 Oct 2021 10:50:57 -0500
Subject: [PATCH] signal: Replace force_sigsegv(SIGSEGV) with
force_fatal_sig(SIGSEGV)

From e349d945fac76bddc78ae1cb92a0145b427a87ce Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Thu, 18 Nov 2021 11:11:13 -0600
Subject: [PATCH] signal: Don't always set SA_IMMUTABLE for forced signals

From fcb116bc43c8c37c052530ead79872f8b2615711 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Thu, 18 Nov 2021 14:23:21 -0600
Subject: [PATCH] signal: Replace force_fatal_sig with force_exit_sig when in doubt

Quoted 3 lines

Quoted 2 lines

Applying them in listed order on top of 5.14.4 and builds/runs on i586, x86_64, armv7hl, aarch64

That series list is crazy, let me go try it and see what blows up! :)

Maybe I am wrong but I think "Don't always set SA_IMMUTABLE for forced signals" will apply if you drop the hunk modifying force_fatal_sig. Then you don't need to backport all of the cleanups just the fix.

Quoted 1 line

I will take a quick look and verify that.

that's why i wrote: "if the other patch for signal that has similar description should land"

(meaning "signal: Replace force_fatal_sig with force_exit_sig when in doubt")

as thats the one needing the whole patch series...

since going by patch descriptions for:

"signal: Don't always set SA_IMMUTABLE for forced signals"

"signal: Replace force_fatal_sig with force_exit_sig when in doubt"

both has the info:

"Unfortunately this broke debuggers[1][2] which reasonably expect to be able to trap synchronous SIGTRAP and SIGSEGV even when the target process is not configured to handle those signals."

and the second even has:
"This avoids userspace regressions as older kernels exited with do_exit which debuggers also can not intercept."

or is the patch description on the second patch somewhat misleading ?

Quoted 6 lines · Thomas Backlund

Den 2021-11-23 kl. 21:24, skrev [email protected]:

Quoted 4 lines

Maybe I am wrong but I think "Don't always set SA_IMMUTABLE for forced signals" will apply if you drop the hunk modifying force_fatal_sig. Then you don't need to backport all of the cleanups just the fix.

Quoted 4 lines

Quoted 1 line

I will take a quick look and verify that.

that's why i wrote: "if the other patch for signal that has similar description should land"

Apologies for not responding to that bit, I was reading quickly and I missed that bit.

The second patch does not need to land in 5.15.

Quoted 19 lines

(meaning "signal: Replace force_fatal_sig with force_exit_sig when in doubt")

as thats the one needing the whole patch series...

since going by patch descriptions for:

"signal: Don't always set SA_IMMUTABLE for forced signals"

"signal: Replace force_fatal_sig with force_exit_sig when in doubt"

both has the info:

"Unfortunately this broke debuggers[1][2] which reasonably expect to be able to trap synchronous SIGTRAP and SIGSEGV even when the target process is not configured to handle those signals."

Quoted 6 lines

and the second even has:
"This avoids userspace regressions as older kernels exited with do_exit which debuggers also can not intercept."

or is the patch description on the second patch somewhat misleading ?

It is the same problem. But it only applies to code that was merged post 5.15.

For 5.15 on force_sig_seccomp is really affected.

For 5.16 there were many calls to do_exit that I turned into signals. Some of the properly should be oridinary signals and some of them for correctness purposes can't allow debuggers or userspace to intercept them.

The second patch went through and modified everything that was non-interceptible before 5.16 to be non-interceptible in 5.16. Where that is not necessary we can relax things later.

But for 5.15 only the one patch needs to be applied.

Eric

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From e349d945fac76bddc78ae1cb92a0145b427a87ce Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <[email protected]>
Date: Thu, 18 Nov 2021 11:11:13 -0600
Subject: [PATCH] signal: Don't always set SA_IMMUTABLE for forced signals

Recently to prevent issues with SECCOMP_RET_KILL and similar signals being changed before they are delivered SA_IMMUTABLE was added.

Unfortunately this broke debuggers[1][2] which reasonably expect to be able to trap synchronous SIGTRAP and SIGSEGV even when the target process is not configured to handle those signals.

Update force_sig_to_task to support both the case when we can allow the debugger to intercept and possibly ignore the signal and the case when it is not safe to let userspace know about the signal until the process has exited.

Suggested-by Linus Torvalds <[email protected]>

Reported-by Kyle Huey <[email protected]>

Reported-by kernel test robot <[email protected]>

Cc [email protected]

[1] https://lkml.kernel.org/r/CAP045AoMY4xf8aC_4QU_-j7obuEPYgTcnQQP3Yxk=2X90jtpjw@mail.gmail.com
[2] https://lkml.kernel.org/r/20211117150258.GB5403@xsang-OptiPlex-9020

Fixes 00b06da29cf9 ("signal: Add SA_IMMUTABLE to ensure forced siganls do not get changed")

Link https://lkml.kernel.org/r/[email protected] open here

Reviewed-by Kees Cook <[email protected]>

Tested-by Kees Cook <[email protected]>

Tested-by Kyle Huey <[email protected]>

Signed-off-by "Eric W. Biederman" <[email protected]>

kernel/signal.c +14 -6

index 7c4b7ae714d4..7815e1bbeddc 100644
@@ -1298,6 +1298,12 @@ int do_send_sig_info(int sig, struct kernel_siginfo *info, struct task_struct *p
        return ret;
 }
 
+enum sig_handler {
+       HANDLER_CURRENT, /* If reachable use the current handler */
+       HANDLER_SIG_DFL, /* Always use SIG_DFL handler semantics */
+       HANDLER_EXIT,    /* Only visible as the process exit code */
+};
+
 /*
  * Force a signal that the process can't ignore: if necessary
  * we unblock the signal and change any SIG_IGN to SIG_DFL.

@@ -1310,7 +1316,8 @@ int do_send_sig_info(int sig, struct kernel_siginfo *info, struct task_struct *p
  * that is why we also clear SIGNAL_UNKILLABLE.
  */
 static int
-force_sig_info_to_task(struct kernel_siginfo *info, struct task_struct *t, bool sigdfl)
+force_sig_info_to_task(struct kernel_siginfo *info, struct task_struct *t,
+       enum sig_handler handler)
 {
        unsigned long int flags;
        int ret, blocked, ignored;

@@ -1321,9 +1328,10 @@ force_sig_info_to_task(struct kernel_siginfo *info, struct task_struct *t, bool
        action = &t->sighand->action[sig-1];
        ignored = action->sa.sa_handler == SIG_IGN;
        blocked = sigismember(&t->blocked, sig);
-       if (blocked || ignored || sigdfl) {
+       if (blocked || ignored || (handler != HANDLER_CURRENT)) {
                action->sa.sa_handler = SIG_DFL;
-               action->sa.sa_flags |= SA_IMMUTABLE;
+               if (handler == HANDLER_EXIT)
+                       action->sa.sa_flags |= SA_IMMUTABLE;
                if (blocked) {
                        sigdelset(&t->blocked, sig);
                        recalc_sigpending_and_wake(t);

@@ -1343,7 +1351,7 @@ force_sig_info_to_task(struct kernel_siginfo *info, struct task_struct *t, bool
 
 int force_sig_info(struct kernel_siginfo *info)
 {
-       return force_sig_info_to_task(info, current, false);
+       return force_sig_info_to_task(info, current, HANDLER_CURRENT);
 }
 
 /*

@@ -1660,7 +1668,7 @@ void force_fatal_sig(int sig)
        info.si_code = SI_KERNEL;
        info.si_pid = 0;
        info.si_uid = 0;
-       force_sig_info_to_task(&info, current, true);
+       force_sig_info_to_task(&info, current, HANDLER_SIG_DFL);
 }
 
 /*

@@ -1693,7 +1701,7 @@ int force_sig_fault_to_task(int sig, int code, void __user *addr
        info.si_flags = flags;
        info.si_isr = isr;
 #endif
-       return force_sig_info_to_task(&info, t, false);
+       return force_sig_info_to_task(&info, t, HANDLER_CURRENT);
 }
 
 int force_sig_fault(int sig, int code, void __user *addr

Since this is taken care of now, AFAICT, I do have one additional question. I reported the regression to LKML a day or so before 5.15.3 was cut. What should I have noticed to see that the regressing changeset was going to 5.15 and where should I have said "hey please don't ship this on 5.15 yet"?

I'd like to know what to do next time :)

Cc: <[email protected]>
Date: Tue, 23 Nov 2021 19:11:53 +0100 (10 hours, 58 minutes, 56 seconds ago)

This is a note to let you know that I've just added the patch titled

exit/syscall_user_dispatch: Send ordinary signals on failure

to the 5.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
exit-syscall_user_dispatch-send-ordinary-signals-on-failure.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 8 lines · Kyle Huey

Since this is taken care of now, AFAICT, I do have one additional question. I reported the regression to LKML a day or so before 5.15.3 was cut. What should I have noticed to see that the regressing changeset was going to 5.15 and where should I have said "hey please don't ship this on 5.15 yet"?

I'd like to know what to do next time :)

When patches are added to the stable tree they are posted for review.

I was Cc'd on a couple of them because of this discussion. The list appear to be "<[email protected]>". Feedback is requested to go to "<[email protected]>". So I believe this conversation is enough to remove the unnecessary patches before they make it to a stable release.

The boiler plate looks like:

Quoted 15 lines

Cc: <[email protected]>
Date: Tue, 23 Nov 2021 19:11:53 +0100 (10 hours, 58 minutes, 56 seconds ago)

This is a note to let you know that I've just added the patch titled

exit/syscall_user_dispatch: Send ordinary signals on failure

to the 5.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
exit-syscall_user_dispatch-send-ordinary-signals-on-failure.patch
and it can be found in the queue-5.15 subdirectory.

Quoted 2 lines

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

I hope that helps.

Eric

Quoted 41 lines · Eric W. Biederman

Quoted 8 lines · Kyle Huey

Since this is taken care of now, AFAICT, I do have one additional question. I reported the regression to LKML a day or so before 5.15.3 was cut. What should I have noticed to see that the regressing changeset was going to 5.15 and where should I have said "hey please don't ship this on 5.15 yet"?

I'd like to know what to do next time :)

When patches are added to the stable tree they are posted for review.

I was Cc'd on a couple of them because of this discussion. The list appear to be "<[email protected]>". Feedback is requested to go to "<[email protected]>". So I believe this conversation is enough to remove the unnecessary patches before they make it to a stable release.

The boiler plate looks like:

Quoted 17 lines

Cc: <[email protected]>
Date: Tue, 23 Nov 2021 19:11:53 +0100 (10 hours, 58 minutes, 56 seconds ago)

This is a note to let you know that I've just added the patch titled

exit/syscall_user_dispatch: Send ordinary signals on failure

to the 5.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
exit-syscall_user_dispatch-send-ordinary-signals-on-failure.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 3 lines

I hope that helps.

Eric

So if I understand this correctly the best (or maybe even only) way to stop a regressing changeset from making it into a stable release is to separately search/watch the stable mailing list for the changeset in question?