Patch "signal/metag: Document a conflict with SI_USER with SIGFPE" has been added to the 4.15-stable tree

From foo@baz Mon Apr 9 10:16:32 CEST 2018

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

signal/metag: Document a conflict with SI_USER with SIGFPE

to the 4.15-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:
signal-metag-document-a-conflict-with-si_user-with-sigfpe.patch
and it can be found in the queue-4.15 subdirectory.

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

From foo@baz Mon Apr 9 10:16:32 CEST 2018
From: "Eric W. Biederman" <[email protected]>
Date: Tue, 1 Aug 2017 10:37:40 -0500
Subject: signal/metag: Document a conflict with SI_USER with SIGFPE

From: "Eric W. Biederman" <[email protected]>

[ Upstream commit b80328be53c215346b153769267b38f531d89b4f ]

Setting si_code to 0 results in a userspace seeing an si_code of 0. This is the same si_code as SI_USER. Posix and common sense requires that SI_USER not be a signal specific si_code. As such this use of 0 for the si_code is a pretty horribly broken ABI.

Further use of si_code == 0 guaranteed that copy_siginfo_to_user saw a value of __SI_KILL and now sees a value of SIL_KILL with the result hat uid and pid fields are copied and which might copying the si_addr field by accident but certainly not by design. Making this a very flakey implementation.

Utilizing FPE_FIXME siginfo_layout will now return SIL_FAULT and the appropriate fields will reliably be copied.

Possible ABI fixes includee:
- Send the signal without siginfo
- Don't generate a signal
- Possibly assign and use an appropriate si_code
- Don't handle cases which can't happen

Cc: James Hogan <[email protected]>
Cc: [email protected]
Ref: ac919f0883e5 ("metag: Traps")

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

Signed-off-by Sasha Levin <[email protected]>

Signed-off-by Greg Kroah-Hartman <[email protected]>

---
 arch/metag/include/uapi/asm/siginfo.h |    7 +++++++
 arch/metag/kernel/traps.c             |    2 +-
 2 files changed, 8 insertions(+), 1 deletion(-)

arch/metag/include/uapi/asm/siginfo.h +7 -0

@@ -6,4 +6,11 @@
 
 #include <asm-generic/siginfo.h>
 
+/*
+ * SIGFPE si_codes
+ */
+#ifdef __KERNEL__
+#define FPE_FIXME      0       /* Broken dup of SI_USER */
+#endif /* __KERNEL__ */
+
 #endif

arch/metag/kernel/traps.c +1 -1

@@ -735,7 +735,7 @@ TBIRES fpe_handler(TBIRES State, int Sig
 	else if (error_state & TXSTAT_FPE_INEXACT_BIT)
 		info.si_code = FPE_FLTRES;
 	else
-		info.si_code = 0;
+		info.si_code = FPE_FIXME;
 	info.si_errno = 0;
 	info.si_addr = (__force void __user *)regs->ctx.CurrPC;
 	force_sig_info(SIGFPE, &info, current);

Patches currently in stable-queue which might be from [email protected] are

queue-4.15/signal-metag-document-a-conflict-with-si_user-with-sigfpe.patch queue-4.15/signal-arm-document-conflicts-with-si_user-and-sigfpe.patch queue-4.15/signal-powerpc-document-conflicts-with-si_user-and-sigfpe-and-sigtrap.patch

Quoted 11 lines · <[email protected]> writes:

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

signal/metag: Document a conflict with SI_USER with SIGFPE

to the 4.15-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:
signal-metag-document-a-conflict-with-si_user-with-sigfpe.patch
and it can be found in the queue-4.15 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.

The patch is a noop functionality wise so I don't see the point of backporting it to stable.