[PATCH 02/16] crypto: cfb - remove bogus memcpy() with src == dest

[Eric Biggers]

From: Eric Biggers <ebigg...@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: <sta...@vger.kernel.org> # v4.17+
Cc: James Bottomley <james.bottom...@hansenpartnership.com>
Signed-off-by: Eric Biggers <ebigg...@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;
 }
 
-- 
2.20.1