lxc-user-nic: fix adding database entries

The code before inserted \0-bytes after every new line which made the db
basically unusable.

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

src/lxc/lxc_user_nic.c

@@ -678,7 +678,7 @@ static char *get_nic_if_avail(int fd, struct alloted_s *names, int pid,
 			      char *intype, char *br, int allowed, char **cnic)
 {
 	int ret;
-	off_t len, slen;
+	size_t slen;
 	char *newline, *nicname, *owner;
 	struct stat sb;
 	struct alloted_s *n;
@@ -693,31 +693,32 @@ static char *get_nic_if_avail(int fd, struct alloted_s *names, int pid,
 
 	owner = names->name;
 
-	if (fstat(fd, &sb) < 0) {
+	ret = fstat(fd, &sb);
+	if (ret < 0) {
 		usernic_error("Failed to fstat: %s\n", strerror(errno));
 		return NULL;
 	}
 
-	len = sb.st_size;
-	if (len > 0) {
-		buf =
-		    mmap(NULL, len, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+	if (sb.st_size > 0) {
+		buf = lxc_strmmap(NULL, sb.st_size, PROT_READ | PROT_WRITE,
+				  MAP_SHARED, fd, 0);
 		if (buf == MAP_FAILED) {
-			usernic_error("Failed to establish shared memory mapping: %s\n",
-				      strerror(errno));
+			usernic_error("Failed to establish shared memory "
+				      "mapping: %s\n", strerror(errno));
 			return NULL;
 		}
 
 		owner = NULL;
 		for (n = names; n != NULL; n = n->next) {
-			count = count_entries(buf, len, n->name, intype, br);
-
+			count = count_entries(buf, sb.st_size, n->name, intype, br);
 			if (count >= n->allowed)
 				continue;
 
 			owner = n->name;
 			break;
 		}
+
+		lxc_strmunmap(buf, sb.st_size);
 	}
 
 	if (owner == NULL)
@@ -729,41 +730,67 @@ static char *get_nic_if_avail(int fd, struct alloted_s *names, int pid,
 		return NULL;
 	}
 
-	/* owner  ' ' intype ' ' br ' ' *nicname + '\n' + '\0' */
-	slen = strlen(owner) + strlen(intype) + strlen(br) + strlen(nicname) + 5;
-	newline = alloca(slen);
+	/* strlen(owner)
+	 * +
+	 * " "
+	 * +
+	 * strlen(intype)
+	 * +
+	 * " "
+	 * +
+	 * strlen(br)
+	 * +
+	 * " "
+	 * +
+	 * strlen(nicname)
+	 * +
+	 * \n
+	 * +
+	 * \0
+	 */
+	slen = strlen(owner) + strlen(intype) + strlen(br) + strlen(nicname) + 4;
+	newline = malloc(slen + 1);
 	if (!newline) {
 		free(nicname);
+		free(newline);
 		usernic_error("Failed allocate memory: %s\n", strerror(errno));
 		return NULL;
 	}
 
-	ret = snprintf(newline, slen, "%s %s %s %s\n", owner, intype, br, nicname);
-	if (ret < 0 || ret >= slen) {
+	ret = snprintf(newline, slen + 1, "%s %s %s %s\n", owner, intype, br, nicname);
+	if (ret < 0 || (size_t)ret >= (slen + 1)) {
 		if (lxc_netdev_delete_by_name(nicname) != 0)
 			usernic_error("Error unlinking %s\n", nicname);
 		free(nicname);
+		free(newline);
 		return NULL;
 	}
-	if (len)
-		munmap(buf, len);
 
-	if (ftruncate(fd, len + slen))
-		usernic_error("Failed to set new file size: %s\n",
-			      strerror(errno));
+	/* Note that the file needs to be truncated to the size **without** the
+	 * \0 byte! Files are not \0-terminated!
+	 */
+	ret = ftruncate(fd, sb.st_size + slen);
+	if (ret < 0)
+		usernic_error("Failed to truncate file: %s\n", strerror(errno));
 
-	buf = mmap(NULL, len + slen, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+	buf = lxc_strmmap(NULL, sb.st_size + slen, PROT_READ | PROT_WRITE,
+			  MAP_SHARED, fd, 0);
 	if (buf == MAP_FAILED) {
 		usernic_error("Failed to establish shared memory mapping: %s\n",
 			      strerror(errno));
 		if (lxc_netdev_delete_by_name(nicname) != 0)
 			usernic_error("Error unlinking %s\n", nicname);
 		free(nicname);
+		free(newline);
 		return NULL;
 	}
 
-	strcpy(buf + len, newline);
-	munmap(buf, len + slen);
+	/* Note that the memory needs to be moved in the buffer **without** the
+	 * \0 byte! Files are not \0-terminated!
+	 */
+	memmove(buf + sb.st_size, newline, slen);
+	free(newline);
+	lxc_strmunmap(buf, sb.st_size + slen);
 
 	return nicname;
 }