Messages in this thread Patch in this message | | | Date | Fri, 24 Nov 2023 10:16:04 -0000 | From | "tip-bot2 for Peter Zijlstra" <> | Subject | [tip: locking/urgent] lockdep: Fix block chain corruption |
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The following commit has been merged into the locking/urgent branch of tip:
Commit-ID: bca4104b00fec60be330cd32818dd5c70db3d469 Gitweb: https://git.kernel.org/tip/bca4104b00fec60be330cd32818dd5c70db3d469 Author: Peter Zijlstra <peterz@infradead.org> AuthorDate: Tue, 21 Nov 2023 12:41:26 +01:00 Committer: Peter Zijlstra <peterz@infradead.org> CommitterDate: Fri, 24 Nov 2023 11:04:54 +01:00
lockdep: Fix block chain corruption
Kent reported an occasional KASAN splat in lockdep. Mark then noted:
> I suspect the dodgy access is to chain_block_buckets[-1], which hits the last 4 > bytes of the redzone and gets (incorrectly/misleadingly) attributed to > nr_large_chain_blocks.
That would mean @size == 0, at which point size_to_bucket() returns -1 and the above happens.
alloc_chain_hlocks() has 'size - req', for the first with the precondition 'size >= rq', which allows the 0.
This code is trying to split a block, del_chain_block() takes what we need, and add_chain_block() puts back the remainder, except in the above case the remainder is 0 sized and things go sideways.
Fixes: 810507fe6fd5 ("locking/lockdep: Reuse freed chain_hlocks entries") Reported-by: Kent Overstreet <kent.overstreet@linux.dev> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Tested-by: Kent Overstreet <kent.overstreet@linux.dev> Link: https://lkml.kernel.org/r/20231121114126.GH8262@noisy.programming.kicks-ass.net --- kernel/locking/lockdep.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index e85b5ad..151bd3d 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -3497,7 +3497,8 @@ static int alloc_chain_hlocks(int req) size = chain_block_size(curr); if (likely(size >= req)) { del_chain_block(0, size, chain_block_next(curr)); - add_chain_block(curr + req, size - req); + if (size > req) + add_chain_block(curr + req, size - req); return curr; } }
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