From c31a871985cac1a594a7e61e7ab808c0f81845ee Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Sun, 31 Mar 2019 13:04:20 -0700 Subject: [PATCH] crypto: cts - don't support empty messages My patches to make testmgr fuzz algorithms against their generic implementation detected that the arm64 implementations of "cts(cbc(aes))" handle empty messages differently from the cts template. Namely, the arm64 implementations forbids (with -EINVAL) all messages shorter than the block size, including the empty message; but the cts template permits empty messages as a special case. No user should be CTS-encrypting/decrypting empty messages, but we need to keep the behavior consistent. Unfortunately, as noted in the source of OpenSSL's CTS implementation [1], there's no common specification for CTS. This makes it somewhat debatable what the behavior should be. However, all CTS specifications seem to agree that messages shorter than the block size are not allowed, and OpenSSL follows this in both CTS conventions it implements. It would also simplify the user-visible semantics to have empty messages no longer be a special case. Therefore, make the cts template return -EINVAL on *all* messages shorter than the block size, including the empty message. [1] https://github.com/openssl/openssl/blob/master/crypto/modes/cts128.c Signed-off-by: Eric Biggers Signed-off-by: Herbert Xu --- crypto/cts.c | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-) diff --git a/crypto/cts.c b/crypto/cts.c index 4e28d83ae37d..9441da797bb9 100644 --- a/crypto/cts.c +++ b/crypto/cts.c @@ -152,12 +152,14 @@ static int crypto_cts_encrypt(struct skcipher_request *req) struct skcipher_request *subreq = &rctx->subreq; int bsize = crypto_skcipher_blocksize(tfm); unsigned int nbytes = req->cryptlen; - int cbc_blocks = (nbytes + bsize - 1) / bsize - 1; unsigned int offset; skcipher_request_set_tfm(subreq, ctx->child); - if (cbc_blocks <= 0) { + if (nbytes < bsize) + return -EINVAL; + + if (nbytes == bsize) { skcipher_request_set_callback(subreq, req->base.flags, req->base.complete, req->base.data); @@ -166,7 +168,7 @@ static int crypto_cts_encrypt(struct skcipher_request *req) return crypto_skcipher_encrypt(subreq); } - offset = cbc_blocks * bsize; + offset = rounddown(nbytes - 1, bsize); rctx->offset = offset; skcipher_request_set_callback(subreq, req->base.flags, @@ -244,13 +246,15 @@ static int crypto_cts_decrypt(struct skcipher_request *req) struct skcipher_request *subreq = &rctx->subreq; int bsize = crypto_skcipher_blocksize(tfm); unsigned int nbytes = req->cryptlen; - int cbc_blocks = (nbytes + bsize - 1) / bsize - 1; unsigned int offset; u8 *space; skcipher_request_set_tfm(subreq, ctx->child); - if (cbc_blocks <= 0) { + if (nbytes < bsize) + return -EINVAL; + + if (nbytes == bsize) { skcipher_request_set_callback(subreq, req->base.flags, req->base.complete, req->base.data); @@ -264,10 +268,10 @@ static int crypto_cts_decrypt(struct skcipher_request *req) space = crypto_cts_reqctx_space(req); - offset = cbc_blocks * bsize; + offset = rounddown(nbytes - 1, bsize); rctx->offset = offset; - if (cbc_blocks <= 1) + if (offset <= bsize) memcpy(space, req->iv, bsize); else scatterwalk_map_and_copy(space, req->src, offset - 2 * bsize,