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Subject[PATCH 5.0 020/238] crypto: cfb - remove bogus memcpy() with src == dest
Date
5.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Biggers <ebiggers@google.com>

commit 6c2e322b3621dc8be72e5c86d4fdb587434ba625 upstream.

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>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
crypto/cfb.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

--- a/crypto/cfb.c
+++ b/crypto/cfb.c
@@ -77,12 +77,14 @@ static int crypto_cfb_encrypt_segment(st
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(st
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(st
src += bsize;
} while ((nbytes -= bsize) >= bsize);

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


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