From b805aebd42364fe696e417808a700fdb9800c9e8 Mon Sep 17 00:00:00 2001 From: Nikita Popov Date: Mon, 9 Aug 2021 20:17:34 +0530 Subject: [PATCH] librt: fix NULL pointer dereference (bug 28213) 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 Upstream-Status: Backport CVE: CVE-2021-38604 Signed-off-by: Armin Kuser --- sysdeps/unix/sysv/linux/mq_notify.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) Index: git/sysdeps/unix/sysv/linux/mq_notify.c =================================================================== --- git.orig/sysdeps/unix/sysv/linux/mq_notify.c +++ git/sysdeps/unix/sysv/linux/mq_notify.c @@ -134,7 +134,7 @@ 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);