From 854fbd6e5f60fe99e8e3a569865409fca378f143 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Thu, 23 Mar 2017 15:46:16 -0700 Subject: [PATCH] lib/syscall: Clear return values when no stack MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Reported-by: Robert Święcki Signed-off-by: Kees Cook Reviewed-by: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Josh Poimboeuf Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: stable@vger.kernel.org # v4.9+ Fixes: aa1f1a639621 ("lib/syscall: Pin the task stack in collect_syscall()") Link: http://lkml.kernel.org/r/20170323224616.GA92694@beast Signed-off-by: Ingo Molnar --- lib/syscall.c | 1 + 1 file changed, 1 insertion(+) diff --git a/lib/syscall.c b/lib/syscall.c index 17d5ff5fa6a3..2c6cd1b5c3ea 100644 --- a/lib/syscall.c +++ b/lib/syscall.c @@ -12,6 +12,7 @@ static int collect_syscall(struct task_struct *target, long *callno, 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; }