Patch "signal/arm: Document conflicts with SI_USER and SIGFPE" has been added to the 3.18-stable tree

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

signal/arm: Document conflicts with SI_USER and SIGFPE

to the 3.18-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-arm-document-conflicts-with-si_user-and-sigfpe.patch
and it can be found in the queue-3.18 subdirectory.

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

From: "Eric W. Biederman" <[email protected]>
Date: Thu, 17 Aug 2017 17:07:46 -0500
Subject: signal/arm: Document conflicts with SI_USER and SIGFPE

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

[ Upstream commit 7771c66457004977b616bab785209f49d164f527 ]

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 that 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 be reliably 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: Russell King <[email protected]>
Cc: [email protected]
Ref: 451436b7bbb2 ("[ARM] Add support code for ARM hardware vector floating point") History Tree: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git

---
 arch/arm/include/uapi/asm/siginfo.h |   13 +++++++++++++
 arch/arm/vfp/vfpmodule.c            |    2 +-
 2 files changed, 14 insertions(+), 1 deletion(-)
 create mode 100644 arch/arm/include/uapi/asm/siginfo.h

@@ -0,0 +1,13 @@
+#ifndef __ASM_SIGINFO_H
+#define __ASM_SIGINFO_H
+
+#include <asm-generic/siginfo.h>
+
+/*
+ * SIGFPE si_codes
+ */
+#ifdef __KERNEL__
+#define FPE_FIXME	0	/* Broken dup of SI_USER */
+#endif /* __KERNEL__ */
+
+#endif

@@ -261,7 +261,7 @@ static void vfp_raise_exceptions(u32 exc
 
 	if (exceptions == VFP_EXCEPTION_ERROR) {
 		vfp_panic("unhandled bounce", inst);
-		vfp_raise_sigfpe(0, regs);
+		vfp_raise_sigfpe(FPE_FIXME, regs);
 		return;
 	}
 

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

queue-3.18/signal-metag-document-a-conflict-with-si_user-with-sigfpe.patch queue-3.18/pidns-disable-pid-allocation-if-pid_ns_prepare_proc-is-failed-in-alloc_pid.patch queue-3.18/signal-arm-document-conflicts-with-si_user-and-sigfpe.patch queue-3.18/signal-powerpc-document-conflicts-with-si_user-and-sigfpe-and-sigtrap.patch