perf: Fix use-after-free in error path

The syscall error path has a use-after-free; put_pmu_ctx() will
reference ctx, therefore we must ensure ctx is destroyed after pmu_ctx
is.

Fixes: bd2756811766 ("perf: Rewrite core context handling")
Reported-by: syzbot+b8e8c01c8ade4fe6e48f@syzkaller.appspotmail.com
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Chengming Zhou <zhouchengming@bytedance.com>
Link: https://lkml.kernel.org/r/Y6B3xEgkbmFUCeni@hirez.programming.kicks-ass.net

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 37c0f04..63d674c 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -12671,7 +12671,8 @@ SYSCALL_DEFINE5(perf_event_open,
        return event_fd;
 
 err_context:
-       /* event->pmu_ctx freed by free_event() */
+       put_pmu_ctx(event->pmu_ctx);
+       event->pmu_ctx = NULL; /* _free_event() */
 err_locked:
        mutex_unlock(&ctx->mutex);
        perf_unpin_context(ctx);
@@ -12784,6 +12785,7 @@ perf_event_create_kernel_counter(struct perf_event_attr *attr, int cpu,
 
 err_pmu_ctx:
        put_pmu_ctx(pmu_ctx);
+       event->pmu_ctx = NULL; /* _free_event() */
 err_unlock:
        mutex_unlock(&ctx->mutex);
        perf_unpin_context(ctx);