On Wed, Nov 16, 2016 at 11:17:33AM -0800, Mat Martineau wrote: > > Herbert - > > Following commit 493b2ed3f7603a15ff738553384d5a4510ffeb95, there is a NULL > dereference crash in algif_hash when recv() is called twice like this: > > send(sk, data, len, MSG_MORE); > recv(sk, hash1, len, 0); > recv(sk, hash2, len, 0); > > In 4.8 and earlier, the two recvs return identical data. In 4.9-rc5, the > second recv triggers this: > > [ 53.041287] BUG: unable to handle kernel NULL pointer dereference at > 0000000000000010 > [ 53.042048] IP: [<ffffffffa73fdfb3>] shash_ahash_digest+0x23/0x130
Ugh. It looks like the shash wrapper is incorrectly dereferencing the SG list even when the length is zero. Rather than fixing it I'm just going to make algif_hash do the safe thing of doing an init followed by a final. Thanks, ---8<--- Subject: crypto: algif_hash - Fix NULL hash crash with shash Recently algif_hash has been changed to allow null hashes. This triggers a bug when used with an shash algorithm whereby it will cause a crash during the digest operation. This patch fixes it by avoiding the digest operation and instead doing an init followed by a final which avoids the buggy code in shash. This patch also ensures that the result buffer is freed after an error so that it is not returned as a genuine hash result on the next recv call. The shash/ahash wrapper code will be fixed later to handle this case correctly. Fixes: 493b2ed3f760 ("crypto: algif_hash - Handle NULL hashes correctly") Signed-off-by: Herbert Xu <herb...@gondor.apana.org.au> diff --git a/crypto/algif_hash.c b/crypto/algif_hash.c index 2d8466f..05e21b4 100644 --- a/crypto/algif_hash.c +++ b/crypto/algif_hash.c @@ -214,23 +214,26 @@ static int hash_recvmsg(struct socket *sock, struct msghdr *msg, size_t len, ahash_request_set_crypt(&ctx->req, NULL, ctx->result, 0); - if (ctx->more) { + if (!result) { + err = af_alg_wait_for_completion( + crypto_ahash_init(&ctx->req), + &ctx->completion); + if (err) + goto unlock; + } + + if (!result || ctx->more) { ctx->more = 0; err = af_alg_wait_for_completion(crypto_ahash_final(&ctx->req), &ctx->completion); if (err) goto unlock; - } else if (!result) { - err = af_alg_wait_for_completion( - crypto_ahash_digest(&ctx->req), - &ctx->completion); } err = memcpy_to_msg(msg, ctx->result, len); - hash_free_result(sk, ctx); - unlock: + hash_free_result(sk, ctx); release_sock(sk); return err ?: len; -- Email: Herbert Xu <herb...@gondor.apana.org.au> Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html