tree 35349236eebaab5b698e4bebe5b4e8019e2e467c
parent da0c9ea146cbe92b832f1b0f694840ea8eb33cce
author Christian Brauner <christian.brauner@ubuntu.com> 1570405936 +0200
committer Christian Brauner <christian.brauner@ubuntu.com> 1570626188 +0200
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taskstats: fix data-race

When assiging and testing taskstats in taskstats_exit() there's a race
when writing and reading sig->stats when a thread-group with more than
one thread exits:

cpu0:
thread catches fatal signal and whole thread-group gets taken down
 do_exit()
 do_group_exit()
 taskstats_exit()
 taskstats_tgid_alloc()
The tasks reads sig->stats holding sighand lock seeing garbage.

cpu1:
task calls exit_group()
 do_exit()
 do_group_exit()
 taskstats_exit()
 taskstats_tgid_alloc()
The task takes sighand lock and assigns new stats to sig->stats.

Fix this by using READ_ONCE() and smp_store_release().

Reported-by: syzbot+c5d03165a1bd1dead0c1@syzkaller.appspotmail.com
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Link: https://lore.kernel.org/r/20191006235216.7483-1-christian.brauner@ubuntu.com
---
/* v1 */
Link: https://lore.kernel.org/r/20191005112806.13960-1-christian.brauner@ubuntu.com

/* v2 */
- Dmitry Vyukov <dvyukov@google.com>, Marco Elver <elver@google.com>:
  - fix the original double-checked locking using memory barriers