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crypto: ofb - fix handling partial blocks and make thread-safe

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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: e497c51896 ("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>
This commit is contained in:
Eric Biggers 2019-01-03 20:16:12 -08:00 committed by Herbert Xu
parent 6c2e322b36
commit b3e3e2db7d
2 changed files with 64 additions and 57 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

95
crypto/ofb.c
View File

@ -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 crypto_skcipher *parent, const u8 *key,
return err;
}
static int crypto_ofb_encrypt_segment(struct crypto_ofb_ctx *ctx,
struct skcipher_walk *walk,
struct crypto_cipher *tfm)
static int crypto_ofb_crypt(struct skcipher_request *req)
{
int bsize = crypto_cipher_blocksize(tfm);
int nbytes = walk->nbytes;
struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
struct crypto_ofb_ctx *ctx = crypto_skcipher_ctx(tfm);
struct crypto_cipher *cipher = ctx->child;
const unsigned int bsize = crypto_cipher_blocksize(cipher);
struct skcipher_walk walk;
int err;
u8 *src = walk->src.virt.addr;
u8 *dst = walk->dst.virt.addr;
u8 *iv = walk->iv;
err = 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 {
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;
crypto_cipher_encrypt_one(cipher, iv, iv);
crypto_xor_cpy(dst, src, iv, bsize);
dst += bsize;
src += bsize;
} while ((nbytes -= bsize) >= bsize);
err = skcipher_walk_done(&walk, nbytes);
}
static int crypto_ofb_encrypt(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;
bsize = crypto_cipher_blocksize(child);
ctx->cnt = bsize;
ret = skcipher_walk_virt(&walk, req, false);
while (walk.nbytes) {
ret = crypto_ofb_encrypt_segment(ctx, &walk, child);
ret = skcipher_walk_done(&walk, ret);
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 ret;
}
/* OFB encrypt and decrypt are identical */
static int crypto_ofb_decrypt(struct skcipher_request *req)
{
return crypto_ofb_encrypt(req);
return err;
}
static int crypto_ofb_init_tfm(struct crypto_skcipher *tfm)
@ -165,12 +143,17 @@ static int crypto_ofb_create(struct crypto_template *tmpl, struct rtattr **tb)
if (err)
goto err_drop_spawn;
inst->alg.base.cra_priority = alg->cra_priority;
inst->alg.base.cra_blocksize = alg->cra_blocksize;
inst->alg.base.cra_alignmask = alg->cra_alignmask;
/* OFB mode is a stream cipher. */
inst->alg.base.cra_blocksize = 1;
/* We access the data as u32s when xoring. */
inst->alg.base.cra_alignmask |= __alignof__(u32) - 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_alignmask = alg->cra_alignmask;
inst->alg.ivsize = alg->cra_blocksize;
inst->alg.min_keysize = alg->cra_cipher.cia_min_keysize;
@ -182,8 +165,8 @@ static int crypto_ofb_create(struct crypto_template *tmpl, struct rtattr **tb)
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;

28
crypto/testmgr.h
View File

@ -16681,8 +16681,7 @@ static const struct cipher_testvec aes_ctr_rfc3686_tv_template[] = {
};
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_ofb_tv_template[] = {
"\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,
}
};