Be more careful when checking for empty files

If we want to avoid reading a totally empty file, it seems better
to check after we have opened the file, not before.

Signed-off-by: Anthony G. Basile <blueness@gentoo.org>

3 files changed, 23 insertions, 7 deletions

diff --git a/src/libudev/util.c b/src/libudev/util.c
index af7477ba6f..116d723a0f 100644
--- a/src/libudev/util.c
+++ b/src/libudev/util.c
@@ -658,6 +658,17 @@ int null_or_empty_path(const char *fn) {
         return null_or_empty(&st);
 }
 
+int null_or_empty_fd(int fd) {
+        struct stat st;
+
+        assert(fd >= 0);
+
+        if (fstat(fd, &st) < 0)
+                return -errno;
+
+        return null_or_empty(&st);
+}
+
 bool dirent_is_file_with_suffix(const struct dirent *de, const char *suffix) {
         assert(de);
 
diff --git a/src/libudev/util.h b/src/libudev/util.h
index bde7b91e6f..a38e8e61c5 100644
--- a/src/libudev/util.h
+++ b/src/libudev/util.h
@@ -222,6 +222,7 @@ int chmod_and_chown(const char *path, mode_t mode, uid_t uid, gid_t gid);
 
 bool null_or_empty(struct stat *st) _pure_;
 int null_or_empty_path(const char *fn);
+int null_or_empty_fd(int fd);
 
 int execute_command(const char *command, char *const argv[]);
 
diff --git a/src/udev/udev-rules.c b/src/udev/udev-rules.c
index 652ac411e1..c47d025846 100644
--- a/src/udev/udev-rules.c
+++ b/src/udev/udev-rules.c
@@ -1538,15 +1538,19 @@ static int parse_file(struct udev_rules *rules, const char *filename)
         int line_nr = 0;
         unsigned int i;
 
-        if (null_or_empty_path(filename)) {
-                log_debug("skip empty file: %s", filename);
-                return 0;
+        f = fopen(filename, "re");
+        if (!f) {
+                if (errno == ENOENT)
+                        return 0;
+                else
+                        return -errno;
         }
-        log_debug("read rules file: %s", filename);
 
-        f = fopen(filename, "re");
-        if (f == NULL)
-                return -1;
+        if (null_or_empty_fd(fileno(f))) {
+                log_debug("Skipping empty file: %s", filename);
+                return 0;
+        } else
+                log_debug("Reading rules file: %s", filename);
 
         first_token = rules->token_cur;
         filename_off = rules_add_string(rules, filename);