diff options
author | Peter Zijlstra <[email protected]> | 2017-03-16 13:47:48 +0100 |
---|---|---|
committer | Ingo Molnar <[email protected]> | 2017-03-16 14:16:52 +0100 |
commit | e552a8389aa409e257b7dcba74f67f128f979ccc (patch) | |
tree | b6202171c50ef57a1a7a5e571a1b162a8b1ddde8 | |
parent | 9d020d33fc1b2faa0eb35859df1381ca5dc94ffe (diff) |
perf/core: Fix use-after-free in perf_release()
Dmitry reported syzcaller tripped a use-after-free in perf_release().
After much puzzlement Oleg spotted the below scenario:
Task1 Task2
fork()
perf_event_init_task()
/* ... */
goto bad_fork_$foo;
/* ... */
perf_event_free_task()
mutex_lock(ctx->lock)
perf_free_event(B)
perf_event_release_kernel(A)
mutex_lock(A->child_mutex)
list_for_each_entry(child, ...) {
/* child == B */
ctx = B->ctx;
get_ctx(ctx);
mutex_unlock(A->child_mutex);
mutex_lock(A->child_mutex)
list_del_init(B->child_list)
mutex_unlock(A->child_mutex)
/* ... */
mutex_unlock(ctx->lock);
put_ctx() /* >0 */
free_task();
mutex_lock(ctx->lock);
mutex_lock(A->child_mutex);
/* ... */
mutex_unlock(A->child_mutex);
mutex_unlock(ctx->lock)
put_ctx() /* 0 */
ctx->task && !TOMBSTONE
put_task_struct() /* UAF */
This patch closes the hole by making perf_event_free_task() destroy the
task <-> ctx relation such that perf_event_release_kernel() will no longer
observe the now dead task.
Spotted-by: Oleg Nesterov <[email protected]>
Reported-by: Dmitry Vyukov <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Stephane Eranian <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Vince Weaver <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Fixes: c6e5b73242d2 ("perf: Synchronously clean up child events")
Link: http://lkml.kernel.org/r/20170314155949.GE32474@worktop
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
-rw-r--r-- | kernel/events/core.c | 11 |
1 files changed, 11 insertions, 0 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c index 1031bdf9f012..4742909c56e6 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -10415,6 +10415,17 @@ void perf_event_free_task(struct task_struct *task) continue; mutex_lock(&ctx->mutex); + raw_spin_lock_irq(&ctx->lock); + /* + * Destroy the task <-> ctx relation and mark the context dead. + * + * This is important because even though the task hasn't been + * exposed yet the context has been (through child_list). + */ + RCU_INIT_POINTER(task->perf_event_ctxp[ctxn], NULL); + WRITE_ONCE(ctx->task, TASK_TOMBSTONE); + put_task_struct(task); /* cannot be last */ + raw_spin_unlock_irq(&ctx->lock); again: list_for_each_entry_safe(event, tmp, &ctx->pinned_groups, group_entry) |