From: Eric Biggers ebiggers@google.com

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

diff --git a/crypto/ofb.c b/crypto/ofb.c index 886631708c5e9..cab0b80953fed 100644 --- 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 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; - - 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) -{ - 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;

- while (walk.nbytes) { - ret = crypto_ofb_encrypt_segment(ctx, &walk, child); - ret = skcipher_walk_done(&walk, ret); - } + do { + crypto_cipher_encrypt_one(cipher, iv, iv); + crypto_xor_cpy(dst, src, iv, bsize); + dst += bsize; + src += bsize; + } while ((nbytes -= bsize) >= bsize);

- return ret; -} + err = skcipher_walk_done(&walk, nbytes); + }

-/* 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 crypto_template *tmpl, struct rtattr **tb) 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 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;

diff --git a/crypto/testmgr.h b/crypto/testmgr.h index 7f4dae7a57a1c..ca8e8ebef309d 100644 --- a/crypto/testmgr.h +++ b/crypto/testmgr.h @@ -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, } };