From: Eric Biggers ebiggers@google.com

Hi Greg, please consider applying this to 4.4-stable and 3.18-stable. It's a minimal fix for a bug that was fixed incidentally by a large refactoring in v4.8.

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In the CTS template, when the input length is <= one block cipher block (e.g. <= 16 bytes for AES) pass the correct length to the underlying CBC transform rather than one block. This matches the upstream behavior and makes the encryption/decryption operation correctly return -EINVAL when 1 <= nbytes < bsize or succeed when nbytes == 0, rather than crashing.

This was fixed upstream incidentally by a large refactoring, commit 0605c41cc53c ("crypto: cts - Convert to skcipher"). But syzkaller easily trips over this when running on older kernels, as it's easily reachable via AF_ALG. Therefore, this patch makes the minimal fix for older kernels.

Cc: linux-crypto@vger.kernel.org Fixes: 76cb9521795a ("[CRYPTO] cts: Add CTS mode required for Kerberos AES support") Signed-off-by: Eric Biggers ebiggers@google.com --- crypto/cts.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/crypto/cts.c b/crypto/cts.c index e467ec0acf9f0..e65688d6a4caa 100644 --- a/crypto/cts.c +++ b/crypto/cts.c @@ -137,8 +137,8 @@ static int crypto_cts_encrypt(struct blkcipher_desc *desc, lcldesc.info = desc->info; lcldesc.flags = desc->flags;

- if (tot_blocks == 1) { - err = crypto_blkcipher_encrypt_iv(&lcldesc, dst, src, bsize); + if (tot_blocks <= 1) { + err = crypto_blkcipher_encrypt_iv(&lcldesc, dst, src, nbytes); } else if (nbytes <= bsize * 2) { err = cts_cbc_encrypt(ctx, desc, dst, src, 0, nbytes); } else { @@ -232,8 +232,8 @@ static int crypto_cts_decrypt(struct blkcipher_desc *desc, lcldesc.info = desc->info; lcldesc.flags = desc->flags;

- if (tot_blocks == 1) { - err = crypto_blkcipher_decrypt_iv(&lcldesc, dst, src, bsize); + if (tot_blocks <= 1) { + err = crypto_blkcipher_decrypt_iv(&lcldesc, dst, src, nbytes); } else if (nbytes <= bsize * 2) { err = cts_cbc_decrypt(ctx, desc, dst, src, 0, nbytes); } else {