Patch "s390/syscalls: Fix out of bounds arguments access" has been added to the 4.4-stable tree

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

s390/syscalls: Fix out of bounds arguments access

to the 4.4-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:
s390-syscalls-fix-out-of-bounds-arguments-access.patch
and it can be found in the queue-4.4 subdirectory.

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

From: Jiri Olsa <[email protected]>
Date: Thu, 29 Jun 2017 11:38:11 +0200
Subject: s390/syscalls: Fix out of bounds arguments access

From: Jiri Olsa <[email protected]>

commit c46fc0424ced3fb71208e72bd597d91b9169a781 upstream.

Zorro reported following crash while having enabled syscall tracing (CONFIG_FTRACE_SYSCALLS):

  Unable to handle kernel pointer dereference at virtual ...
  Oops: 0011 [#1] SMP DEBUG_PAGEALLOC

SNIP

  Call Trace:
  ([<000000000024d79c>] ftrace_syscall_enter+0xec/0x1d8)
   [<00000000001099c6>] do_syscall_trace_enter+0x236/0x2f8
   [<0000000000730f1c>] sysc_tracesys+0x1a/0x32
   [<000003fffcf946a2>] 0x3fffcf946a2
  INFO: lockdep is turned off.
  Last Breaking-Event-Address:
   [<000000000022dd44>] rb_event_data+0x34/0x40
  ---[ end trace 8c795f86b1b3f7b9 ]---

The crash happens in syscall_get_arguments function for syscalls with zero arguments, that will try to access first argument (args[0]) in event entry, but it's not allocated.

Bail out of there are no arguments.

---
 arch/s390/include/asm/syscall.h |    6 ++++++
 1 file changed, 6 insertions(+)

@@ -64,6 +64,12 @@ static inline void syscall_get_arguments
 {
 	unsigned long mask = -1UL;
 
+	/*
+	 * No arguments for this syscall, there's nothing to do.
+	 */
+	if (!n)
+		return;
+
 	BUG_ON(i + n > 6);
 #ifdef CONFIG_COMPAT
 	if (test_tsk_thread_flag(task, TIF_31BIT))

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

queue-4.4/s390-syscalls-fix-out-of-bounds-arguments-access.patch