Messages in this thread Patch in this message | | | From | Mark Rutland <> | Subject | [PATCH] Detect early free of a live mm | Date | Wed, 28 Feb 2018 12:14:58 +0000 |
| |
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
| |