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 <herbert@xxxxxxxxxxxxxxxxxxx>
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 <herbert@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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