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* [PATCH] Detect early free of a live mm
@ 2018-02-28 12:14 Mark Rutland
  2018-02-28 12:18 ` Mark Rutland
                   ` (2 more replies)
  0 siblings, 3 replies; 10+ messages in thread
From: Mark Rutland @ 2018-02-28 12:14 UTC (permalink / raw)
  To: linux-kernel
  Cc: Mark Rutland, Andrew Morton, Ingo Molnar, Mathieu Desnoyers,
	Michal Hocko, Peter Zijlstra, Rik van Riel, Will Deacon

KASAN splats indicate that in some cases we free a live mm, then
continue to access it, with potentially disastrous results. This is
likely due to a mismatched mmdrop() somewhere in the kernel, but so far
the culprit remains elusive.

Let's have __mmdrop() verify that the mm isn't live for the current
task, similar to the existing check for init_mm. This way, we can catch
this class of issue earlier, and without requiring KASAN.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Zijlstra <peterz@infraded.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
---
 kernel/fork.c | 2 ++
 1 file changed, 2 insertions(+)

Hi,

For context, we're seeing an intermittent use-after-free of an mm on
arm64 [1], where it looks like an mm has been freed earlier than
expected. So far KASAN has only caught legitimate mmdrop() uses, where
mm_count is presumably already bogus.

Mark.

[1] https://lkml.kernel.org/r/20180214120254.qq4w4s42ecxio7lu@lakrids.cambridge.arm.com

diff --git a/kernel/fork.c b/kernel/fork.c
index e5d9d405ae4e..6922d93551b8 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -595,6 +595,8 @@ static void check_mm(struct mm_struct *mm)
 void __mmdrop(struct mm_struct *mm)
 {
 	BUG_ON(mm == &init_mm);
+	BUG_ON(mm == current->mm);
+	BUG_ON(mm == current->active_mm);
 	mm_free_pgd(mm);
 	destroy_context(mm);
 	hmm_mm_destroy(mm);
-- 
2.11.0

^ permalink raw reply related	[flat|nested] 10+ messages in thread

end of thread, other threads:[~2018-03-12 13:46 UTC | newest]

Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-02-28 12:14 [PATCH] Detect early free of a live mm Mark Rutland
2018-02-28 12:18 ` Mark Rutland
2018-03-01  9:35   ` Michal Hocko
2018-03-01 11:22     ` Mark Rutland
2018-03-01 12:40       ` Michal Hocko
2018-03-01 12:49         ` Mark Rutland
2018-03-02  1:16 ` Andrew Morton
2018-03-02 10:24   ` Mark Rutland
2018-03-09 21:11 ` 94d3a25408: kernel_BUG_at_kernel/fork.c kernel test robot
2018-03-12 13:46   ` Mark Rutland

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