From: Eric Biggers ebiggers@google.com

All the ChaCha20 algorithms as well as the ARM bit-sliced AES-XTS algorithms call skcipher_walk_virt(), then access the IV (walk.iv) before checking whether any bytes need to be processed (walk.nbytes).

But if the input is empty, then skcipher_walk_virt() doesn't set the IV, and the algorithms crash trying to use the uninitialized IV pointer.

Fix it by setting the IV earlier in skcipher_walk_virt(). Also fix it for the AEAD walk functions.

This isn't a perfect solution because we can't actually align the IV to ->cra_alignmask unless there are bytes to process, for one because the temporary buffer for the aligned IV is freed by skcipher_walk_done(), which is only called when there are bytes to process. Thus, algorithms that require aligned IVs will still need to avoid accessing the IV when walk.nbytes == 0. Still, many algorithms/architectures are fine with IVs having any alignment, and even for those that aren't, a misaligned pointer bug is much less severe than an uninitialized pointer bug.

This change also matches the behavior of the older blkcipher_walk API.

Fixes: 0cabf2af6f5a ("crypto: skcipher - Fix crash on zero-length input") Reported-by: syzbot syzkaller@googlegroups.com Cc: stable@vger.kernel.org # v4.14+ Signed-off-by: Eric Biggers ebiggers@google.com --- crypto/skcipher.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/crypto/skcipher.c b/crypto/skcipher.c index 778e0ff42bfa..11af5fd6a443 100644 --- a/crypto/skcipher.c +++ b/crypto/skcipher.c @@ -449,6 +449,8 @@ static int skcipher_walk_skcipher(struct skcipher_walk *walk,

walk->total = req->cryptlen; walk->nbytes = 0; + walk->iv = req->iv; + walk->oiv = req->iv;

if (unlikely(!walk->total)) return 0; @@ -456,9 +458,6 @@ static int skcipher_walk_skcipher(struct skcipher_walk *walk, scatterwalk_start(&walk->in, req->src); scatterwalk_start(&walk->out, req->dst);

- walk->iv = req->iv; - walk->oiv = req->iv; - walk->flags &= ~SKCIPHER_WALK_SLEEP; walk->flags |= req->base.flags & CRYPTO_TFM_REQ_MAY_SLEEP ? SKCIPHER_WALK_SLEEP : 0; @@ -510,6 +509,8 @@ static int skcipher_walk_aead_common(struct skcipher_walk *walk, int err;

walk->nbytes = 0; + walk->iv = req->iv; + walk->oiv = req->iv;

if (unlikely(!walk->total)) return 0; @@ -525,9 +526,6 @@ static int skcipher_walk_aead_common(struct skcipher_walk *walk, scatterwalk_done(&walk->in, 0, walk->total); scatterwalk_done(&walk->out, 0, walk->total);

- walk->iv = req->iv; - walk->oiv = req->iv; - if (req->base.flags & CRYPTO_TFM_REQ_MAY_SLEEP) walk->flags |= SKCIPHER_WALK_SLEEP; else