Re: [PATCH] uprobes: Fix NULL pointer dereference in hprobe_expire()

On Thu, 30 Jul 2026 12:38:24 +0200
Peter Zijlstra [off-list ref] wrote:

On Thu, Jul 30, 2026 at 08:54:21AM +0900, Masami Hiramatsu wrote:

quoted

On Wed, 29 Jul 2026 12:31:08 -0700
Andrii Nakryiko [off-list ref] wrote:

quoted

On Wed, Jul 29, 2026 at 9:02 AM Oleg Nesterov [off-list ref] wrote:

quoted

On 07/29, Breno Leitao wrote:

quoted

--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c

@@ -832,7 +832,7 @@ static struct uprobe *hprobe_expire(struct hprobe *hprobe, bool get)
              if (try_cmpxchg(&hprobe->state, &hstate, uprobe ? HPROBE_STABLE : HPROBE_GONE)) {
                      /* We won the race, we are the ones to unlock SRCU */
                      __srcu_read_unlock(&uretprobes_srcu, hprobe->srcu_idx);
-                     return get ? get_uprobe(uprobe) : uprobe;
+                     return get && uprobe ? get_uprobe(uprobe) : uprobe;

Well, looks "obviously correct". At least the current code is obviously
wrong, it even checks uprobe != NULL 3 lines above.

Andrii ?

Yes, indeed, I'm more surprised this didn't come up much earlier
(probably it's rare enough to have uretprobe with refcnt at zero
during fork). The fix looks good, thanks!

Acked-by: Andrii Nakryiko <andrii@kernel.org>

quoted

Acked-by: Oleg Nesterov <oleg@redhat.com>

Thanks, this seems good to me. (uprobe is NULL checked in try_cmpxchg(),
so it could be NULL.)

Can I pick this to probes/fixes branch?

tip/perf/urgent ?

Either way works. Can we update MAINTAINERS file if you will maintain
uprobe in tip tree?

Thank you,

-- 
Masami Hiramatsu (Google) [off-list ref]