[PATCH 4.4,4.9] crypto: arm/aes-neonbs - don't access already-freed walk.iv

[Eric Biggers <ebiggers@kernel.org>]

From: Eric Biggers <ebiggers@google.com>

commit 767f015ea0b7ab9d60432ff6cd06b664fd71f50f upstream.
[Please apply to 4.9-stable and earlier.]

If the user-provided IV needs to be aligned to the algorithm's
alignmask, then skcipher_walk_virt() copies the IV into a new aligned
buffer walk.iv.  But skcipher_walk_virt() can fail afterwards, and then
if the caller unconditionally accesses walk.iv, it's a use-after-free.

arm32 xts-aes-neonbs doesn't set an alignmask, so currently it isn't
affected by this despite unconditionally accessing walk.iv.  However
this is more subtle than desired, and it was actually broken prior to
the alignmask being removed by commit cc477bf64573 ("crypto: arm/aes -
replace bit-sliced OpenSSL NEON code").  Thus, update xts-aes-neonbs to
start checking the return value of skcipher_walk_virt().

Fixes: e4e7f10bfc40 ("ARM: add support for bit sliced AES using NEON instructions")
Cc: <stable@vger.kernel.org> # v3.13+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
---
 arch/arm/crypto/aesbs-glue.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/arm/crypto/aesbs-glue.c b/arch/arm/crypto/aesbs-glue.c
index 5d934a0039d76..cb2486a526e66 100644
--- a/arch/arm/crypto/aesbs-glue.c
+++ b/arch/arm/crypto/aesbs-glue.c
@@ -265,6 +265,8 @@ static int aesbs_xts_encrypt(struct blkcipher_desc *desc,
 
 	blkcipher_walk_init(&walk, dst, src, nbytes);
 	err = blkcipher_walk_virt_block(desc, &walk, 8 * AES_BLOCK_SIZE);
+	if (err)
+		return err;
 
 	/* generate the initial tweak */
 	AES_encrypt(walk.iv, walk.iv, &ctx->twkey);
@@ -289,6 +291,8 @@ static int aesbs_xts_decrypt(struct blkcipher_desc *desc,
 
 	blkcipher_walk_init(&walk, dst, src, nbytes);
 	err = blkcipher_walk_virt_block(desc, &walk, 8 * AES_BLOCK_SIZE);
+	if (err)
+		return err;
 
 	/* generate the initial tweak */
 	AES_encrypt(walk.iv, walk.iv, &ctx->twkey);
-- 
2.21.0.1020.gf2820cf01a-goog