diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2022-05-20 20:38:06 +0200 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2022-05-20 08:44:00 -1000 |
| commit | 3ac6487e584a1eb54071dbe1212e05b884136704 (patch) | |
| tree | 07b3b0617e264ae3ef5d188275e7991120859ee2 /kernel/events | |
| parent | 3b5e1590a26713a8c76896f0f1b99f52ec24e72f (diff) | |
perf: Fix sys_perf_event_open() race against self
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>
Diffstat (limited to 'kernel/events')
| -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 7858bafffa9d..7f1e4c5897e7 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -12217,6 +12217,9 @@ 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; @@ -12282,6 +12285,7 @@ SYSCALL_DEFINE5(perf_event_open, } else { perf_event_ctx_unlock(group_leader, gctx); move_group = 0; + goto not_move_group; } } @@ -12298,7 +12302,17 @@ 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; |