crypto: cts - fix crash on short inputs

[It's a minimal fix for a bug that was fixed incidentally by a large
refactoring in v4.8.]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/crypto/cts.c b/crypto/cts.c
index e467ec0..e65688d 100644 (file)
--- 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 {