[PATCH] crypto: drbg: check blocklen is non zero

[trix]

From: Tom Rix <trix@xxxxxxxxxx>

Clang static analysis reports this error

crypto/drbg.c:441:40: warning: Division by zero
        padlen = (inputlen + sizeof(L_N) + 1) % (drbg_blocklen(drbg));
                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~

When drbg_bocklen fails it returns 0.

	if (drbg && drbg->core)
		return drbg->core->blocklen_bytes;
	return 0;

In many places in drbg_ctr_df drbg_bocklen is assumed to be non zero.
So turn the assumption into a check.

Fixes: 541af946fe13 ("crypto: drbg - SP800-90A Deterministic Random Bit Generator")

Signed-off-by: Tom Rix <trix@xxxxxxxxxx>
---
 crypto/drbg.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/crypto/drbg.c b/crypto/drbg.c
index e99fe34cfa00..bd9a137e5473 100644
--- a/crypto/drbg.c
+++ b/crypto/drbg.c
@@ -420,6 +420,9 @@ static int drbg_ctr_df(struct drbg_state *drbg,
 	size_t inputlen = 0;
 	struct drbg_string *seed = NULL;
 
+	if (!drbg_blocklen(drbg))
+		return -EINVAL;
+
 	memset(pad, 0, drbg_blocklen(drbg));
 	memset(iv, 0, drbg_blocklen(drbg));
 
-- 
2.18.1