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

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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>
This commit is contained in:
Vinayak Menon 2018-03-28 16:01:16 -07:00 committed by Linus Torvalds
parent b213b54fbf
commit 914b6dfff7
1 changed files with 7 additions and 5 deletions
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12
mm/kmemleak.c
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@ -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();