[ccan] [PATCH 4/7] crypto/hmac_sha256: Remove undefined memset()

[David Gibson]

A memset() with a zero length argument isn't well defined.  It *might* be
a no-op, but then it might not.  So, test for this case in
hmac_sha256_init().

Found by Coverity.

Signed-off-by: David Gibson <david at gibson.dropbear.id.au>
---
 ccan/crypto/hmac_sha256/hmac_sha256.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/ccan/crypto/hmac_sha256/hmac_sha256.c b/ccan/crypto/hmac_sha256/hmac_sha256.c
index 0392afe..70ca3b2 100644
--- a/ccan/crypto/hmac_sha256/hmac_sha256.c
+++ b/ccan/crypto/hmac_sha256/hmac_sha256.c
@@ -36,7 +36,9 @@ void hmac_sha256_init(struct hmac_sha256_ctx *ctx,
 	 *   appended with 44 zero bytes 0x00)
 	 */
 	memcpy(k_ipad, k, ksize);
-	memset((char *)k_ipad + ksize, 0, HMAC_SHA256_BLOCKSIZE - ksize);
+	if (ksize < HMAC_SHA256_BLOCKSIZE)
+		memset((char *)k_ipad + ksize, 0,
+		       HMAC_SHA256_BLOCKSIZE - ksize);
 
 	/*
 	 * (2) XOR (bitwise exclusive-OR) the B byte string computed
-- 
2.9.3