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

Overview

In the Linux kernel, the following vulnerability has been resolved:

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

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.

Affected

• Linux >= 33d2f09fcb357fd1861c4959d1d3505492bf91f8 < 9a0dab8a9d9975dec14a118b55cae2517aea5ca9
• Linux >= 33d2f09fcb357fd1861c4959d1d3505492bf91f8 < 962ce265fbf5d87afeb78cf19c12e083ab0ffeb8
• Linux >= 33d2f09fcb357fd1861c4959d1d3505492bf91f8 < a1a875614dae43b43d311bb9e7a7a70eed78efe6
• Linux >= 33d2f09fcb357fd1861c4959d1d3505492bf91f8 < 40ea7dfa8cd5f9aed72a55c9ca3008aee5880e6f
• Linux >= 33d2f09fcb357fd1861c4959d1d3505492bf91f8 < 3195e0daf590683992edb4eed32269e569e04924
• Linux 4.12

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.