ubifs: fix wrong use of crypto_shash_descsize()

crypto_shash_descsize() returns the size of the shash_desc context
needed to compute the hash, not the size of the hash itself.

crypto_shash_digestsize() would be correct, or alternatively using
c->hash_len and c->hmac_desc_len which already store the correct values.
But actually it's simpler to just use stack arrays, so do that instead.

Fixes: 49525e5e ("ubifs: Add helper functions for authentication support")
Fixes: da8ef65f ("ubifs: Authenticate replayed journal")
Cc: <stable@vger.kernel.org> # v4.20+
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Richard Weinberger <richard@nod.at>

fs/ubifs/auth.c

@@ -79,13 +79,9 @@ int ubifs_prepare_auth_node(struct ubifs_info *c, void *node,
 			     struct shash_desc *inhash)
 {
 	struct ubifs_auth_node *auth = node;
-	u8 *hash;
+	u8 hash[UBIFS_HASH_ARR_SZ];
 	int err;
 
-	hash = kmalloc(crypto_shash_descsize(c->hash_tfm), GFP_NOFS);
-	if (!hash)
-		return -ENOMEM;
-
 	{
 		SHASH_DESC_ON_STACK(hash_desc, c->hash_tfm);
 
@@ -94,21 +90,16 @@ int ubifs_prepare_auth_node(struct ubifs_info *c, void *node,
 
 		err = crypto_shash_final(hash_desc, hash);
 		if (err)
-			goto out;
+			return err;
 	}
 
 	err = ubifs_hash_calc_hmac(c, hash, auth->hmac);
 	if (err)
-		goto out;
+		return err;
 
 	auth->ch.node_type = UBIFS_AUTH_NODE;
 	ubifs_prepare_node(c, auth, ubifs_auth_node_sz(c), 0);
-
-	err = 0;
-out:
-	kfree(hash);
-
-	return err;
+	return 0;
 }
 
 static struct shash_desc *ubifs_get_desc(const struct ubifs_info *c,

fs/ubifs/replay.c

@@ -601,18 +601,12 @@ static int authenticate_sleb(struct ubifs_info *c, struct ubifs_scan_leb *sleb,
 	struct ubifs_scan_node *snod;
 	int n_nodes = 0;
 	int err;
-	u8 *hash, *hmac;
+	u8 hash[UBIFS_HASH_ARR_SZ];
+	u8 hmac[UBIFS_HMAC_ARR_SZ];
 
 	if (!ubifs_authenticated(c))
 		return sleb->nodes_cnt;
 
-	hash = kmalloc(crypto_shash_descsize(c->hash_tfm), GFP_NOFS);
-	hmac = kmalloc(c->hmac_desc_len, GFP_NOFS);
-	if (!hash || !hmac) {
-		err = -ENOMEM;
-		goto out;
-	}
-
 	list_for_each_entry(snod, &sleb->nodes, list) {
 
 		n_nodes++;
@@ -662,9 +656,6 @@ static int authenticate_sleb(struct ubifs_info *c, struct ubifs_scan_leb *sleb,
 		err = 0;
 	}
 out:
-	kfree(hash);
-	kfree(hmac);
-
 	return err ? err : n_nodes - n_not_auth;
 }