diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2022-05-20 20:38:06 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2022-05-25 09:17:55 +0200 |
| commit | 3ee8e109c3c316073a3e0f83ec0769c7ee8a7375 (patch) | |
| tree | a9d7952b8417c071d105848b7034522b36fa8bb1 /kernel | |
| parent | 18fb7d533c79909675749f1795dc312246143c6d (diff) | |
perf: Fix sys_perf_event_open() race against self
commit 3ac6487e584a1eb54071dbe1212e05b884136704 upstream.
Norbert reported that it's possible to race sys_perf_event_open() such
that the looser ends up in another context from the group leader,
triggering many WARNs.
The move_group case checks for races against itself, but the
!move_group case doesn't, seemingly relying on the previous
group_leader->ctx == ctx check. However, that check is racy due to not
holding any locks at that time.
Therefore, re-check the result after acquiring locks and bailing
if they no longer match.
Additionally, clarify the not_move_group case from the
move_group-vs-move_group race.
Fixes: f63a8daa5812 ("perf: Fix event->ctx locking")
Reported-by: Norbert Slusarek <nslusarek@gmx.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/events/core.c | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c index 9aa6563587d8..8ba155a7b59e 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -11946,6 +11946,9 @@ SYSCALL_DEFINE5(perf_event_open, * Do not allow to attach to a group in a different task * or CPU context. If we're moving SW events, we'll fix * this up later, so allow that. + * + * Racy, not holding group_leader->ctx->mutex, see comment with + * perf_event_ctx_lock(). */ if (!move_group && group_leader->ctx != ctx) goto err_context; @@ -12013,6 +12016,7 @@ SYSCALL_DEFINE5(perf_event_open, } else { perf_event_ctx_unlock(group_leader, gctx); move_group = 0; + goto not_move_group; } } @@ -12029,7 +12033,17 @@ SYSCALL_DEFINE5(perf_event_open, } } else { mutex_lock(&ctx->mutex); + + /* + * Now that we hold ctx->lock, (re)validate group_leader->ctx == ctx, + * see the group_leader && !move_group test earlier. + */ + if (group_leader && group_leader->ctx != ctx) { + err = -EINVAL; + goto err_locked; + } } +not_move_group: if (ctx->task == TASK_TOMBSTONE) { err = -ESRCH; |