scan-build: fix zero size memory allocation

MEM04-C, CWE-131: result of malloc(0) is implementation specific

src/common/hex.c

@@ -15,6 +15,7 @@
 */
 
 #include <config.h>
+#include <assert.h>
 #include <ctype.h>
 #include <stdint.h>
 #include <stdlib.h>
@@ -27,10 +28,11 @@
  */
 static uint8_t hex_to_num(int c)
 {
-	if (c >= '0' && c <= '9')
+	if (c >= '0' && c <= '9') {
 		return c - '0';
-	else
+	} else {
 		return c - 'a' + 10;
+	}
 }
 
 /*!
@@ -38,7 +40,7 @@ static uint8_t hex_to_num(int c)
  */
 int hex_decode(const char *input, uint8_t **output, size_t *output_size)
 {
-	if (!input || !output || !output_size) {
+	if (!input || input[0] == '\0' || !output || !output_size) {
 		return KNOT_EINVAL;
 	}
 
@@ -58,7 +60,8 @@ int hex_decode(const char *input, uint8_t **output, size_t *output_size)
 	// output allocation
 
 	size_t result_size = input_size / 2;
-	uint8_t *result = malloc(result_size * sizeof(uint8_t));
+	assert(result_size > 0);
+	uint8_t *result = malloc(result_size);
 	if (!result) {
 		return KNOT_ENOMEM;
 	}

src/libknot/dnssec/nsec3.c

@@ -51,7 +51,7 @@ static int nsec3_sha1(const uint8_t *salt, uint8_t salt_length,
 	assert(digest);
 	assert(digest_size);
 
-	if (!salt) {
+	if (salt_length > 0 && !salt) {
 		return KNOT_EINVAL;
 	}
 

src/utils/nsec3hash/nsec3hash_main.c

@@ -64,22 +64,26 @@ static bool parse_nsec3_params(knot_nsec3_params_t *params, const char *salt,
 		return false;
 	}
 
-	size_t salt_length;
-	result = hex_decode(salt, &params->salt, &salt_length);
-	if (result != KNOT_EOK) {
-		fprintf(stderr, "Invalid salt: %s\n",
-		        knot_strerror(result));
-		return false;
+	size_t salt_length = 0;
+	uint8_t *salt_data = NULL;
+
+	if (salt[0] != '\0') {
+		result = hex_decode(salt, &salt_data, &salt_length);
+		if (result != KNOT_EOK) {
+			fprintf(stderr, "Invalid salt: %s\n",
+				knot_strerror(result));
+			return false;
+		}
 	}
 
 	if (salt_length > UINT8_MAX) {
 		fprintf(stderr, "Invalid salt: Maximal length is %d bytes.\n",
 		        UINT8_MAX);
-		free(params->salt);
-		memset(params, '\0', sizeof(*params));
+		free(salt_data);
 		return false;
 	}
 
+	params->salt = salt_data;
 	params->salt_length = (uint8_t)salt_length;
 
 	return true;
@@ -180,7 +184,6 @@ int main(int argc, char *argv[])
 	       nsec3_params.iterations);
 
 fail:
-
 	knot_nsec3_params_free(&nsec3_params);
 	knot_dname_free(&dname);
 	free(digest);