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@gondor.apana.org.au>
Tested-by: Laura Abbott <labbott@redhat.com>

1 files changed, 10 insertions, 7 deletions

diff --git a/crypto/algif_hash.c b/crypto/algif_hash.c
index 2d8466f9e49b..05e21b464433 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;