dm-crypt: reject the lmk IV mode with AEAD ciphers

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A "capi:" table line that pairs an AEAD cipher with the lmk IV mode,
for example "capi:gcm(aes)-lmk" with the integrity:28:aead option,
causes an oops when it is loaded. lmk sets tfms_count to 64, but
crypt_alloc_tfms_aead only allocates one transform, so crypt_setkey
reads past the end of the tfms_aead array and calls crypto_aead_setkey
on the values it finds there.

lmk exists for compatibility with Loop-AES, which uses CBC, so refuse
it with an AEAD cipher rather than allocate 64 AEAD transforms. The
check cannot go in crypt_iv_lmk_ctr with the other lmk checks, because
the IV constructor runs after crypt_set_key.

Note that this is not a security bug because the memory corruption can
only be triggered by root.

Fixes: 33d2f09fcb ("dm crypt: introduce new format of cipher with "capi:" prefix")
Cc: stable@vger.kernel.org
Signed-off-by: Ben Cressey <ben@cressey.dev>
Assisted-by: LLM
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

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Ben Cressey 2026-09-15 00:39:10 +00:00 • committed by Mikulas Patocka

parent 764b683a61

commit 3195e0daf5

1 changed files with 6 additions and 1 deletions

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drivers/md/dm-crypt.c

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