From c69f990e356dd8e756b0025e026d59db5af6e059 Mon Sep 17 00:00:00 2001 From: Nikita Popov Date: Mon, 9 Aug 2021 17:15:52 +0500 Subject: [PATCH] librt: fix NULL pointer dereference (bug 28213) To: libc-alpha@sourceware.org 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). --- 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 (¬ify_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); -- 2.17.1