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 <rob...@swiecki.net>
Fixes: aa1f1a639621 ("lib/syscall: Pin the task stack in collect_syscall()")
Cc: sta...@vger.kernel.org # v4.9+
Signed-off-by: Kees Cook <keesc...@chromium.org>
---
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;
}
--
2.7.4
--
Kees Cook
Pixel Security
