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dm-crypt: fix a tiny race condition in crypt_dec_pending

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crypt_dec_pending reads io->error before calling atomic_dec_and_test.
Another context, for example crypt_endio called from an interrupt, may
set io->error and drop its reference between the read and the
decrement. crypt_dec_pending then drops the last reference and completes
the bio with the stale status - so a read that failed and was never
decrypted, or a write that failed, is reported as successful.

The read was placed before the decrement by commit b35f8caa08 ("dm
crypt: wait for endio to complete before destruction"), because that
commit freed dm_crypt_io before calling bio_endio. This is no longer the
case, dm_crypt_io lives in the per-bio data now.

Read io->error after atomic_dec_and_test instead. atomic_dec_and_test is
fully ordered, so no additional barrier is needed.

Fixes: b35f8caa08 ("dm crypt: wait for endio to complete before destruction")
Cc: stable@vger.kernel.org
Reviewed-by: Jose Fernandez (Anthropic) <jose.fernandez@linux.dev>
Signed-off-by: Ben Cressey <ben@cressey.dev>
Assisted-by: Claude:unspecified
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
This commit is contained in:
Ben Cressey 2026-08-26 00:25:33 +00:00 committed by Mikulas Patocka
parent cee9395acd
commit 148845aa19
1 changed files with 1 additions and 2 deletions
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3
drivers/md/dm-crypt.c
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@ -1745,7 +1745,6 @@ static void crypt_dec_pending(struct dm_crypt_io *io)
{
struct crypt_config *cc = io->cc;
struct bio *base_bio = io->base_bio;
blk_status_t error = io->error;
if (!atomic_dec_and_test(&io->io_pending))
return;
@ -1767,7 +1766,7 @@ static void crypt_dec_pending(struct dm_crypt_io *io)
else
kfree(io->integrity_metadata);
base_bio->bi_status = error;
base_bio->bi_status = io->error;
bio_endio(base_bio);
}