Patch "lib/syscall: Clear return values when no stack" has been added to the 4.9-stable tree

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

lib/syscall: Clear return values when no stack

to the 4.9-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:
lib-syscall-clear-return-values-when-no-stack.patch
and it can be found in the queue-4.9 subdirectory.

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

From: Kees Cook <[email protected]>
Date: Thu, 23 Mar 2017 15:46:16 -0700
Subject: lib/syscall: Clear return values when no stack
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From: Kees Cook <[email protected]>

commit 854fbd6e5f60fe99e8e3a569865409fca378f143 upstream.

Commit:

aa1f1a639621 ("lib/syscall: Pin the task stack in collect_syscall()")

... added logic to handle a process stack not existing, but left sp and pc uninitialized, which can be later reported via /proc/$pid/syscall for zombie processes, potentially exposing kernel memory to userspace.

Zombie /proc/$pid/syscall before:
-1 0xffffffff9a060100 0xffff92f42d6ad900

Zombie /proc/$pid/syscall after:
-1 0x0 0x0

---
 lib/syscall.c |    1 +
 1 file changed, 1 insertion(+)

@@ -11,6 +11,7 @@ static int collect_syscall(struct task_s
 
 	if (!try_get_task_stack(target)) {
 		/* Task has no stack, so the task isn't in a syscall. */
+		*sp = *pc = 0;
 		*callno = -1;
 		return 0;
 	}

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

queue-4.9/x86-mm-kaslr-exclude-efi-region-from-kaslr-va-space-randomization.patch queue-4.9/lib-syscall-clear-return-values-when-no-stack.patch