[PATCH] Potential NULL pointer deference in drbg_ctr_df

[Stephan Mueller <smueller@chronox.de>]

The handling of additional input data / personalization string data may
be subject to a NULL pointer deference for the CTR DRBG. The
caller-provided data may be NULL which must be caught by the DRBG.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Stephan Mueller <smueller@chronox.de>
---
 crypto/drbg.c | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/crypto/drbg.c b/crypto/drbg.c
index faaa2ce..8e7c302 100644
--- a/crypto/drbg.c
+++ b/crypto/drbg.c
@@ -513,17 +513,20 @@ static int drbg_ctr_df(struct drbg_state *drbg,
 	drbg_string_fill(&S2, L_N, sizeof(L_N));
 	drbg_string_fill(&S4, pad, padlen);
 	S1.next = &S2;
-	S2.next = addtl;
 
-	/*
-	 * splice in addtl between S2 and S4 -- we place S4 at the end of the
-	 * input data chain
-	 */
-	tempstr = addtl;
-	for (; NULL != tempstr; tempstr = tempstr->next)
-		if (NULL == tempstr->next)
-			break;
-	tempstr->next = &S4;
+	if (NULL == addtl) {
+		S2.next = &S4;
+	} else {
+		/*
+		 * splice in addtl between S2 and S4 -- we place S4 at the end
+		 * of the input data chain
+		 */
+		S2.next = addtl;
+		tempstr = addtl;
+		while (tempstr->next)
+			tempstr = tempstr->next;
+		tempstr->next = &S4;
+	}
 
 	/* 10.4.2 step 9 */
 	while (templen < (drbg_keylen(drbg) + (drbg_blocklen(drbg)))) {
-- 
1.9.3