From: Eric Biggers ebiggers@google.com

The memcpy() in crypto_cfb_decrypt_inplace() uses walk->iv as both the source and destination, which has undefined behavior. It is unneeded because walk->iv is already used to hold the previous ciphertext block; thus, walk->iv is already updated to its final value. So, remove it.

Also, note that in-place decryption is the only case where the previous ciphertext block is not directly available. Therefore, as a related cleanup I also updated crypto_cfb_encrypt_segment() to directly use the previous ciphertext block rather than save it into walk->iv. This makes it consistent with in-place encryption and out-of-place decryption; now only in-place decryption is different, because it has to be.

Fixes: a7d85e06ed80 ("crypto: cfb - add support for Cipher FeedBack mode") Cc: stable@vger.kernel.org # v4.17+ Cc: James Bottomley James.Bottomley@HansenPartnership.com Signed-off-by: Eric Biggers ebiggers@google.com --- crypto/cfb.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/crypto/cfb.c b/crypto/cfb.c index 183e8a9c33128..4abfe32ff8451 100644 --- a/crypto/cfb.c +++ b/crypto/cfb.c @@ -77,12 +77,14 @@ static int crypto_cfb_encrypt_segment(struct skcipher_walk *walk, do { crypto_cfb_encrypt_one(tfm, iv, dst); crypto_xor(dst, src, bsize); - memcpy(iv, dst, bsize); + iv = dst;

src += bsize; dst += bsize; } while ((nbytes -= bsize) >= bsize);

+ memcpy(walk->iv, iv, bsize); + return nbytes; }

@@ -162,7 +164,7 @@ static int crypto_cfb_decrypt_inplace(struct skcipher_walk *walk, const unsigned int bsize = crypto_cfb_bsize(tfm); unsigned int nbytes = walk->nbytes; u8 *src = walk->src.virt.addr; - u8 *iv = walk->iv; + u8 * const iv = walk->iv; u8 tmp[MAX_CIPHER_BLOCKSIZE];

do { @@ -172,8 +174,6 @@ static int crypto_cfb_decrypt_inplace(struct skcipher_walk *walk, src += bsize; } while ((nbytes -= bsize) >= bsize);

- memcpy(walk->iv, iv, bsize); - return nbytes; }