Commit 914b6dff authored Mar 28, 2018 by Vinayak Menon Committed by Linus Torvalds Mar 28, 2018

mm/kmemleak.c: wait for scan completion before disabling free

A crash is observed when kmemleak_scan accesses the object->pointer,
likely due to the following race.

  TASK A             TASK B                     TASK C
  kmemleak_write
   (with "scan" and
   NOT "scan=on")
  kmemleak_scan()
                     create_object
                     kmem_cache_alloc fails
                     kmemleak_disable
                     kmemleak_do_cleanup
                     kmemleak_free_enabled = 0
                                                kfree
                                                kmemleak_free bails out
                                                 (kmemleak_free_enabled is 0)
                                                slub frees object->pointer
  update_checksum
  crash - object->pointer
   freed (DEBUG_PAGEALLOC)

kmemleak_do_cleanup waits for the scan thread to complete, but not for
direct call to kmemleak_scan via kmemleak_write.  So add a wait for
kmemleak_scan completion before disabling kmemleak_free, and while at it
fix the comment on stop_scan_thread.

[vinmenon@codeaurora.org: fix stop_scan_thread comment]
  Link: http://lkml.kernel.org/r/1522219972-22809-1-git-send-email-vinmenon@codeaurora.org
Link: http://lkml.kernel.org/r/1522063429-18992-1-git-send-email-vinmenon@codeaurora.org


Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent b213b54f

mm/kmemleak.c

+7 −5

Original line number	Diff line number	Diff line
		@@ -1657,8 +1657,7 @@ static void start_scan_thread(void)
		}

		/*
		* Stop the automatic memory scanning thread. This function must be called
		* with the scan_mutex held.
		* Stop the automatic memory scanning thread.
		*/
		static void stop_scan_thread(void)
		{
		@@ -1921,12 +1920,15 @@ static void kmemleak_do_cleanup(struct work_struct *work)
		{
		stop_scan_thread();

		mutex_lock(&scan_mutex);
		/*
		* Once the scan thread has stopped, it is safe to no longer track
		* object freeing. Ordering of the scan thread stopping and the memory
		* accesses below is guaranteed by the kthread_stop() function.
		* Once it is made sure that kmemleak_scan has stopped, it is safe to no
		* longer track object freeing. Ordering of the scan thread stopping and
		* the memory accesses below is guaranteed by the kthread_stop()
		* function.
		*/
		kmemleak_free_enabled = 0;
		mutex_unlock(&scan_mutex);

		if (!kmemleak_found_leaks)
		__kmemleak_do_cleanup();

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