KEYS: DH: forbid using digest_null as the KDF hash

Requesting "digest_null" in the keyctl_kdf_params caused an infinite
loop in kdf_ctr() because the "null" hash has a digest size of 0.  Fix
it by rejecting hash algorithms with a digest size of 0.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: James Morris <james.l.morris@oracle.com>

1 files changed, 11 insertions, 1 deletions

diff --git a/security/keys/dh.c b/security/keys/dh.c
index e603bd912e4c..8abc70ebe22d 100644
--- a/security/keys/dh.c
+++ b/security/keys/dh.c
@@ -89,6 +89,7 @@ static int kdf_alloc(struct kdf_sdesc **sdesc_ret, char *hashname)
         struct crypto_shash *tfm;
         struct kdf_sdesc *sdesc;
         int size;
+        int err;
 
         /* allocate synchronous hash */
         tfm = crypto_alloc_shash(hashname, 0, 0);
@@ -97,16 +98,25 @@ static int kdf_alloc(struct kdf_sdesc **sdesc_ret, char *hashname)
                 return PTR_ERR(tfm);
         }
 
+        err = -EINVAL;
+        if (crypto_shash_digestsize(tfm) == 0)
+                goto out_free_tfm;
+
+        err = -ENOMEM;
         size = sizeof(struct shash_desc) + crypto_shash_descsize(tfm);
         sdesc = kmalloc(size, GFP_KERNEL);
         if (!sdesc)
-                return -ENOMEM;
+                goto out_free_tfm;
         sdesc->shash.tfm = tfm;
         sdesc->shash.flags = 0x0;
 
         *sdesc_ret = sdesc;
 
         return 0;
+
+out_free_tfm:
+        crypto_free_shash(tfm);
+        return err;
 }
 
 static void kdf_dealloc(struct kdf_sdesc *sdesc)