From b3e3e2db7de4a1ffe8845876c3520b866cd48de1 Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Thu, 3 Jan 2019 20:16:12 -0800 Subject: crypto: ofb - fix handling partial blocks and make thread-safe 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: # v4.20+ Cc: Gilad Ben-Yossef Signed-off-by: Eric Biggers Reviewed-by: Gilad Ben-Yossef Signed-off-by: Herbert Xu --- crypto/ofb.c | 91 ++++++++++++++++++++++++------------------------------------ 1 file changed, 37 insertions(+), 54 deletions(-) (limited to 'crypto/ofb.c') diff --git a/crypto/ofb.c b/crypto/ofb.c index 886631708c5e..cab0b80953fe 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 @@ -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; -- cgit v1.2.3-59-g8ed1b