sockets: avoid string truncation warnings when copying UNIX path

In file included from /usr/include/string.h:494,
                 from include/qemu/osdep.h:101,
                 from util/qemu-sockets.c:18:
In function ‘strncpy’,
    inlined from ‘unix_connect_saddr.isra.0’ at util/qemu-sockets.c:925:5:
/usr/include/bits/string_fortified.h:106:10: warning: ‘__builtin_strncpy’ specified bound 108 equals destination size [-Wstringop-truncation]
  106 |   return __builtin___strncpy_chk (__dest, __src, __len, __bos (__dest));
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In function ‘strncpy’,
    inlined from ‘unix_listen_saddr.isra.0’ at util/qemu-sockets.c:880:5:
/usr/include/bits/string_fortified.h:106:10: warning: ‘__builtin_strncpy’ specified bound 108 equals destination size [-Wstringop-truncation]
  106 |   return __builtin___strncpy_chk (__dest, __src, __len, __bos (__dest));
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We are already validating the UNIX socket path length earlier in
the functions. If we save this string length when we first check
it, then we can simply use memcpy instead of strcpy later, avoiding
the gcc truncation warnings.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Message-Id: <20190501145052.12579-1-berrange@redhat.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
(cherry picked from commit 2d2023c3b99edb33ad4bb9791f70456ea1a1c049)

diff --git a/util/qemu-sockets.c b/util/qemu-sockets.c
index 97050516900020bfc4caabf53433ea3f083d5627..ba6335e71a95188c7e3e42d6dc93586bbbfd67cd 100644 (file)
--- a/util/qemu-sockets.c
+++ b/util/qemu-sockets.c
@@ -830,6 +830,7 @@ static int unix_listen_saddr(UnixSocketAddress *saddr,
     int sock, fd;
     char *pathbuf = NULL;
     const char *path;
+    size_t pathlen;
 
     sock = qemu_socket(PF_UNIX, SOCK_STREAM, 0);
     if (sock < 0) {
@@ -845,7 +846,8 @@ static int unix_listen_saddr(UnixSocketAddress *saddr,
         path = pathbuf = g_strdup_printf("%s/qemu-socket-XXXXXX", tmpdir);
     }
 
-    if (strlen(path) > sizeof(un.sun_path)) {
+    pathlen = strlen(path);
+    if (pathlen > sizeof(un.sun_path)) {
         error_setg(errp, "UNIX socket path '%s' is too long", path);
         error_append_hint(errp, "Path must be less than %zu bytes\n",
                           sizeof(un.sun_path));
@@ -877,7 +879,7 @@ static int unix_listen_saddr(UnixSocketAddress *saddr,
 
     memset(&un, 0, sizeof(un));
     un.sun_family = AF_UNIX;
-    strncpy(un.sun_path, path, sizeof(un.sun_path));
+    memcpy(un.sun_path, path, pathlen);
 
     if (bind(sock, (struct sockaddr*) &un, sizeof(un)) < 0) {
         error_setg_errno(errp, errno, "Failed to bind socket to %s", path);
@@ -901,6 +903,7 @@ static int unix_connect_saddr(UnixSocketAddress *saddr, Error **errp)
 {
     struct sockaddr_un un;
     int sock, rc;
+    size_t pathlen;
 
     if (saddr->path == NULL) {
         error_setg(errp, "unix connect: no path specified");
@@ -913,7 +916,8 @@ static int unix_connect_saddr(UnixSocketAddress *saddr, Error **errp)
         return -1;
     }
 
-    if (strlen(saddr->path) > sizeof(un.sun_path)) {
+    pathlen = strlen(saddr->path);
+    if (pathlen > sizeof(un.sun_path)) {
         error_setg(errp, "UNIX socket path '%s' is too long", saddr->path);
         error_append_hint(errp, "Path must be less than %zu bytes\n",
                           sizeof(un.sun_path));
@@ -922,7 +926,7 @@ static int unix_connect_saddr(UnixSocketAddress *saddr, Error **errp)
 
     memset(&un, 0, sizeof(un));
     un.sun_family = AF_UNIX;
-    strncpy(un.sun_path, saddr->path, sizeof(un.sun_path));
+    memcpy(un.sun_path, saddr->path, pathlen);
 
     /* connect to peer */
     do {