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From: Matt Fleming <>
To: Sebastian Andrzej Siewior <>
	Daniel Wagner <>,
	Matt Fleming <>
Subject: [PATCH RT] signal: Prevent double-free of user struct
Date: Tue,  7 Apr 2020 10:54:13 +0100
Message-ID: <> (raw)

The way user struct reference counting works changed significantly with,

  fda31c50292a ("signal: avoid double atomic counter increments for user accounting")

Now user structs are only freed once the last pending signal is
dequeued. Make sigqueue_free_current() follow this new convention to
avoid freeing the user struct multiple times and triggering this

 refcount_t: underflow; use-after-free.
 WARNING: CPU: 0 PID: 6794 at lib/refcount.c:288 refcount_dec_not_one+0x45/0x50
 Call Trace:
  ? schedule_hrtimeout_range_clock+0x104/0x110

Signed-off-by: Matt Fleming <>
Reported-by: Daniel Wagner <>
 kernel/signal.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index 267fce07df5d..3651483bd4d8 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -494,8 +494,8 @@ static void sigqueue_free_current(struct sigqueue *q)
 	up = q->user;
 	if (rt_prio(current->normal_prio) && !put_task_cache(current, q)) {
-		atomic_dec(&up->sigpending);
-		free_uid(up);
+		if (atomic_dec_and_test(&up->sigpending))
+			free_uid(up);
 	} else

             reply index

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-07  9:54 Matt Fleming [this message]
2020-04-15 16:46 ` Sebastian Andrzej Siewior
2020-04-15 19:05   ` Daniel Wagner
2020-04-16  8:05     ` Sebastian Andrzej Siewior
2020-04-07 14:45 Markus Elfring

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