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Subject[PATCH 5.0 021/238] crypto: ofb - fix handling partial blocks and make thread-safe
Date
5.0-stable review patch.  If anyone has any objections, please let me know.

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

From: Eric Biggers <ebiggers@google.com>

commit b3e3e2db7de4a1ffe8845876c3520b866cd48de1 upstream.

Fix multiple bugs in the OFB implementation:

1. It stored the per-request state 'cnt' in the tfm context, which can be
used by multiple threads concurrently (e.g. via AF_ALG).
2. It didn't support messages not a multiple of the block cipher size,
despite being a stream cipher.
3. It didn't set cra_blocksize to 1 to indicate it is a stream cipher.

To fix these, set the 'chunksize' property to the cipher block size to
guarantee that when walking through the scatterlist, a partial block can
only occur at the end. Then change the implementation to XOR a block at
a time at first, then XOR the partial block at the end if needed. This
is the same way CTR and CFB are implemented. As a bonus, this also
improves performance in most cases over the current approach.

Fixes: e497c51896b3 ("crypto: ofb - add output feedback mode")
Cc: <stable@vger.kernel.org> # v4.20+
Cc: Gilad Ben-Yossef <gilad@benyossef.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Gilad Ben-Yossef <gilad@benyossef.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
crypto/ofb.c | 91 ++++++++++++++++++++++---------------------------------
crypto/testmgr.h | 28 +++++++++++++++-
2 files changed, 63 insertions(+), 56 deletions(-)

--- a/crypto/ofb.c
+++ b/crypto/ofb.c
@@ -5,9 +5,6 @@
*
* Copyright (C) 2018 ARM Limited or its affiliates.
* All rights reserved.
- *
- * Based loosely on public domain code gleaned from libtomcrypt
- * (https://github.com/libtom/libtomcrypt).
*/

#include <crypto/algapi.h>
@@ -21,7 +18,6 @@

struct crypto_ofb_ctx {
struct crypto_cipher *child;
- int cnt;
};


@@ -41,58 +37,40 @@ static int crypto_ofb_setkey(struct cryp
return err;
}

-static int crypto_ofb_encrypt_segment(struct crypto_ofb_ctx *ctx,
- struct skcipher_walk *walk,
- struct crypto_cipher *tfm)
-{
- int bsize = crypto_cipher_blocksize(tfm);
- int nbytes = walk->nbytes;
-
- u8 *src = walk->src.virt.addr;
- u8 *dst = walk->dst.virt.addr;
- u8 *iv = walk->iv;
-
- do {
- if (ctx->cnt == bsize) {
- if (nbytes < bsize)
- break;
- crypto_cipher_encrypt_one(tfm, iv, iv);
- ctx->cnt = 0;
- }
- *dst = *src ^ iv[ctx->cnt];
- src++;
- dst++;
- ctx->cnt++;
- } while (--nbytes);
- return nbytes;
-}
-
-static int crypto_ofb_encrypt(struct skcipher_request *req)
+static int crypto_ofb_crypt(struct skcipher_request *req)
{
- struct skcipher_walk walk;
struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
- unsigned int bsize;
struct crypto_ofb_ctx *ctx = crypto_skcipher_ctx(tfm);
- struct crypto_cipher *child = ctx->child;
- int ret = 0;
+ struct crypto_cipher *cipher = ctx->child;
+ const unsigned int bsize = crypto_cipher_blocksize(cipher);
+ struct skcipher_walk walk;
+ int err;

- bsize = crypto_cipher_blocksize(child);
- ctx->cnt = bsize;
+ err = skcipher_walk_virt(&walk, req, false);

- ret = skcipher_walk_virt(&walk, req, false);
+ while (walk.nbytes >= bsize) {
+ const u8 *src = walk.src.virt.addr;
+ u8 *dst = walk.dst.virt.addr;
+ u8 * const iv = walk.iv;
+ unsigned int nbytes = walk.nbytes;
+
+ do {
+ crypto_cipher_encrypt_one(cipher, iv, iv);
+ crypto_xor_cpy(dst, src, iv, bsize);
+ dst += bsize;
+ src += bsize;
+ } while ((nbytes -= bsize) >= bsize);

- while (walk.nbytes) {
- ret = crypto_ofb_encrypt_segment(ctx, &walk, child);
- ret = skcipher_walk_done(&walk, ret);
+ err = skcipher_walk_done(&walk, nbytes);
}

- return ret;
-}
-
-/* OFB encrypt and decrypt are identical */
-static int crypto_ofb_decrypt(struct skcipher_request *req)
-{
- return crypto_ofb_encrypt(req);
+ if (walk.nbytes) {
+ crypto_cipher_encrypt_one(cipher, walk.iv, walk.iv);
+ crypto_xor_cpy(walk.dst.virt.addr, walk.src.virt.addr, walk.iv,
+ walk.nbytes);
+ err = skcipher_walk_done(&walk, 0);
+ }
+ return err;
}

static int crypto_ofb_init_tfm(struct crypto_skcipher *tfm)
@@ -165,13 +143,18 @@ static int crypto_ofb_create(struct cryp
if (err)
goto err_drop_spawn;

+ /* OFB mode is a stream cipher. */
+ inst->alg.base.cra_blocksize = 1;
+
+ /*
+ * To simplify the implementation, configure the skcipher walk to only
+ * give a partial block at the very end, never earlier.
+ */
+ inst->alg.chunksize = alg->cra_blocksize;
+
inst->alg.base.cra_priority = alg->cra_priority;
- inst->alg.base.cra_blocksize = alg->cra_blocksize;
inst->alg.base.cra_alignmask = alg->cra_alignmask;

- /* We access the data as u32s when xoring. */
- inst->alg.base.cra_alignmask |= __alignof__(u32) - 1;
-
inst->alg.ivsize = alg->cra_blocksize;
inst->alg.min_keysize = alg->cra_cipher.cia_min_keysize;
inst->alg.max_keysize = alg->cra_cipher.cia_max_keysize;
@@ -182,8 +165,8 @@ static int crypto_ofb_create(struct cryp
inst->alg.exit = crypto_ofb_exit_tfm;

inst->alg.setkey = crypto_ofb_setkey;
- inst->alg.encrypt = crypto_ofb_encrypt;
- inst->alg.decrypt = crypto_ofb_decrypt;
+ inst->alg.encrypt = crypto_ofb_crypt;
+ inst->alg.decrypt = crypto_ofb_crypt;

inst->free = crypto_ofb_free;

--- a/crypto/testmgr.h
+++ b/crypto/testmgr.h
@@ -16681,8 +16681,7 @@ static const struct cipher_testvec aes_c
};

static const struct cipher_testvec aes_ofb_tv_template[] = {
- /* From NIST Special Publication 800-38A, Appendix F.5 */
- {
+ { /* From NIST Special Publication 800-38A, Appendix F.5 */
.key = "\x2b\x7e\x15\x16\x28\xae\xd2\xa6"
"\xab\xf7\x15\x88\x09\xcf\x4f\x3c",
.klen = 16,
@@ -16705,6 +16704,31 @@ static const struct cipher_testvec aes_o
"\x30\x4c\x65\x28\xf6\x59\xc7\x78"
"\x66\xa5\x10\xd9\xc1\xd6\xae\x5e",
.len = 64,
+ .also_non_np = 1,
+ .np = 2,
+ .tap = { 31, 33 },
+ }, { /* > 16 bytes, not a multiple of 16 bytes */
+ .key = "\x2b\x7e\x15\x16\x28\xae\xd2\xa6"
+ "\xab\xf7\x15\x88\x09\xcf\x4f\x3c",
+ .klen = 16,
+ .iv = "\x00\x01\x02\x03\x04\x05\x06\x07"
+ "\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f",
+ .ptext = "\x6b\xc1\xbe\xe2\x2e\x40\x9f\x96"
+ "\xe9\x3d\x7e\x11\x73\x93\x17\x2a"
+ "\xae",
+ .ctext = "\x3b\x3f\xd9\x2e\xb7\x2d\xad\x20"
+ "\x33\x34\x49\xf8\xe8\x3c\xfb\x4a"
+ "\x77",
+ .len = 17,
+ }, { /* < 16 bytes */
+ .key = "\x2b\x7e\x15\x16\x28\xae\xd2\xa6"
+ "\xab\xf7\x15\x88\x09\xcf\x4f\x3c",
+ .klen = 16,
+ .iv = "\x00\x01\x02\x03\x04\x05\x06\x07"
+ "\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f",
+ .ptext = "\x6b\xc1\xbe\xe2\x2e\x40\x9f",
+ .ctext = "\x3b\x3f\xd9\x2e\xb7\x2d\xad",
+ .len = 7,
}
};


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