On 11/17/2016 06:07 AM, Herbert Xu wrote:
> 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;
>
Confirmed to work for me. You can take that as a Tested-by.
Thanks,
Laura
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