linux-kernel - [PATCH 3.16 036/132] crypto: salsa20 - don't access already-freed walk.iv

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Message-ID: <lsq.1568989415.620662485@decadent.org.uk>
Date:   Fri, 20 Sep 2019 15:23:35 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Herbert Xu" <herbert@...dor.apana.org.au>,
        "Eric Biggers" <ebiggers@...gle.com>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>
Subject: [PATCH 3.16 036/132] crypto: salsa20 - don't access already-freed
 walk.iv

3.16.74-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Biggers <ebiggers@...gle.com>

commit edaf28e996af69222b2cb40455dbb5459c2b875a upstream.

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.

salsa20-generic 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 b62b3db76f73 ("crypto: salsa20-generic - cleanup
and convert to skcipher API").

Since salsa20-generic does not update the IV and does not need any IV
alignment, update it to use req->iv instead of walk.iv.

Fixes: 2407d60872dd ("[CRYPTO] salsa20: Salsa20 stream cipher")
Signed-off-by: Eric Biggers <ebiggers@...gle.com>
Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 crypto/salsa20_generic.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/crypto/salsa20_generic.c
+++ b/crypto/salsa20_generic.c
@@ -186,7 +186,7 @@ static int encrypt(struct blkcipher_desc
 	blkcipher_walk_init(&walk, dst, src, nbytes);
 	err = blkcipher_walk_virt_block(desc, &walk, 64);

-	salsa20_ivsetup(ctx, walk.iv);
+	salsa20_ivsetup(ctx, desc->info);

 	while (walk.nbytes >= 64) {
 		salsa20_encrypt_bytes(ctx, walk.dst.virt.addr,