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* [committed 2.34] librt: fix NULL pointer dereference (bug 28213)
@ 2021-08-09 14:52 Siddhesh Poyarekar
  0 siblings, 0 replies; only message in thread
From: Siddhesh Poyarekar @ 2021-08-09 14:52 UTC (permalink / raw)
  To: libc-stable; +Cc: Nikita Popov

From: Nikita Popov <>

Helper thread frees copied attribute on NOTIFY_REMOVED message
received from the OS kernel.  Unfortunately, it fails to check whether
copied attribute actually exists (data.attr != NULL).  This worked
earlier because free() checks passed pointer before actually
attempting to release corresponding memory.  But
__pthread_attr_destroy assumes pointer is not NULL.

So passing NULL pointer to __pthread_attr_destroy will result in
segmentation fault.  This scenario is possible if
notification->sigev_notify_attributes == NULL (which means default
thread attributes should be used).

Signed-off-by: Nikita Popov <>
Reviewed-by: Siddhesh Poyarekar <>
(cherry picked from commit b805aebd42364fe696e417808a700fdb9800c9e8)
 sysdeps/unix/sysv/linux/mq_notify.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sysdeps/unix/sysv/linux/mq_notify.c b/sysdeps/unix/sysv/linux/mq_notify.c
index 9799dcdaa4..eccae2e4c6 100644
--- a/sysdeps/unix/sysv/linux/mq_notify.c
+++ b/sysdeps/unix/sysv/linux/mq_notify.c
@@ -131,7 +131,7 @@ helper_thread (void *arg)
 	       to wait until it is done with it.  */
 	    (void) __pthread_barrier_wait (&notify_barrier);
-      else if (data.raw[NOTIFY_COOKIE_LEN - 1] == NOTIFY_REMOVED)
+      else if (data.raw[NOTIFY_COOKIE_LEN - 1] == NOTIFY_REMOVED && data.attr != NULL)
 	  /* The only state we keep is the copy of the thread attributes.  */
 	  __pthread_attr_destroy (data.attr);

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2021-08-09 14:52 [committed 2.34] librt: fix NULL pointer dereference (bug 28213) Siddhesh Poyarekar

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