[PATCH v1] tools: fix usage of strncpy

* [PATCH v1] tools: fix usage of strncpy
@ 2020-06-08  7:28 Olaf Hering
  2020-06-08  8:00 ` Olaf Hering
  0 siblings, 1 reply; 9+ messages in thread
From: Olaf Hering @ 2020-06-08  7:28 UTC (permalink / raw)
  To: xen-devel; +Cc: Anthony PERARD, Olaf Hering, Ian Jackson, Wei Liu

In case of truncation no trailing zero will be added to the target
string. Reduce the amount of bytes to copy by one to make sure a
trailing zero always exists.

In file included from /usr/include/string.h:495,
                 from libxl_internal.h:38,
                 from libxl_utils.c:20:
In function 'strncpy',
    inlined from 'libxl__prepare_sockaddr_un' at libxl_utils.c:1262:5:
/usr/include/bits/string_fortified.h:106:10: error: '__builtin_strncpy' specified bound 108 equals destination size [-Werror=stringop-truncation]
  106 |   return __builtin___strncpy_chk (__dest, __src, __len, __bos (__dest));
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors

Signed-off-by: Olaf Hering <olaf@aepfle.de>
---

gcc may not detect the off-by-one error in libxl__prepare_sockaddr_un, fix the strncpy usage anyway.

 tools/libvchan/vchan-socket-proxy.c | 8 ++++----
 tools/libxl/libxl_utils.c           | 2 +-
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/tools/libvchan/vchan-socket-proxy.c b/tools/libvchan/vchan-socket-proxy.c
index 13700c5d67..b312f05ca7 100644
--- a/tools/libvchan/vchan-socket-proxy.c
+++ b/tools/libvchan/vchan-socket-proxy.c
@@ -140,7 +140,7 @@ static int set_nonblocking(int fd, int nonblocking) {
 static int connect_socket(const char *path_or_fd) {
     int fd;
     char *endptr;
-    struct sockaddr_un addr;
+    struct sockaddr_un addr = {};
 
     fd = strtoll(path_or_fd, &endptr, 0);
     if (*endptr == '\0') {
@@ -153,7 +153,7 @@ static int connect_socket(const char *path_or_fd) {
         return -1;
 
     addr.sun_family = AF_UNIX;
-    strncpy(addr.sun_path, path_or_fd, sizeof(addr.sun_path));
+    strncpy(addr.sun_path, path_or_fd, sizeof(addr.sun_path) - 1);
     if (connect(fd, (const struct sockaddr *)&addr, sizeof(addr)) == -1) {
         close(fd);
         return -1;
@@ -167,7 +167,7 @@ static int connect_socket(const char *path_or_fd) {
 static int listen_socket(const char *path_or_fd) {
     int fd;
     char *endptr;
-    struct sockaddr_un addr;
+    struct sockaddr_un addr = {};
 
     fd = strtoll(path_or_fd, &endptr, 0);
     if (*endptr == '\0') {
@@ -180,7 +180,7 @@ static int listen_socket(const char *path_or_fd) {
         return -1;
 
     addr.sun_family = AF_UNIX;
-    strncpy(addr.sun_path, path_or_fd, sizeof(addr.sun_path));
+    strncpy(addr.sun_path, path_or_fd, sizeof(addr.sun_path) - 1);
     if (bind(fd, (const struct sockaddr *)&addr, sizeof(addr)) == -1) {
         close(fd);
         return -1;
diff --git a/tools/libxl/libxl_utils.c b/tools/libxl/libxl_utils.c
index f360f5e228..83592e829d 100644
--- a/tools/libxl/libxl_utils.c
+++ b/tools/libxl/libxl_utils.c
@@ -1259,7 +1259,7 @@ int libxl__prepare_sockaddr_un(libxl__gc *gc,
     }
     memset(un, 0, sizeof(struct sockaddr_un));
     un->sun_family = AF_UNIX;
-    strncpy(un->sun_path, path, sizeof(un->sun_path));
+    strncpy(un->sun_path, path, sizeof(un->sun_path) - 1);
     return 0;
 }
 


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