[PATCH 1/5] KEYS: DH: forbid using digest_null as the KDF hash

[Eric Biggers]

From: Eric Biggers <ebigg...@google.com>

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 <ebigg...@google.com>
---
 security/keys/dh.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

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)
-- 
2.12.2