fs-util: add access_fd() which is like access() but for fds

Linux doesn't have faccess(), hence let's emulate it. Linux has access()
and faccessat() but neither allows checking the access rights of an fd
passed in directly.

diff --git a/src/basic/fs-util.c b/src/basic/fs-util.c
index 946f779a329b1b583b22459c4defcf88aee7f3c5..ff8b4e8747dc4c54cd02a26e515dcd83d211c157 100644 (file)
--- a/src/basic/fs-util.c
+++ b/src/basic/fs-util.c
@@ -104,7 +104,6 @@ int rmdir_parents(const char *path, const char *stop) {
         return 0;
 }
 
-
 int rename_noreplace(int olddirfd, const char *oldpath, int newdirfd, const char *newpath) {
         struct stat buf;
         int ret;
@@ -809,3 +808,18 @@ int chase_symlinks(const char *path, const char *original_root, unsigned flags,
 
         return exists;
 }
+
+int access_fd(int fd, int mode) {
+        char p[strlen("/proc/self/fd/") + DECIMAL_STR_MAX(fd) + 1];
+        int r;
+
+        /* Like access() but operates on an already open fd */
+
+        xsprintf(p, "/proc/self/fd/%i", fd);
+
+        r = access(p, mode);
+        if (r < 0)
+                r = -errno;
+
+        return r;
+}

diff --git a/src/basic/fs-util.h b/src/basic/fs-util.h
index d3342d5cdaadff288c4911c2e214a15ca96d395a..9849522f5af1000870a7a738e5fe07748327dacd 100644 (file)
--- a/src/basic/fs-util.h
+++ b/src/basic/fs-util.h
@@ -98,3 +98,5 @@ static inline void unlink_and_free(char *p) {
         free(p);
 }
 DEFINE_TRIVIAL_CLEANUP_FUNC(char*, unlink_and_free);
+
+int access_fd(int fd, int mode);

diff --git a/src/test/test-fs-util.c b/src/test/test-fs-util.c
index a5871a25b061636dbcdde043e49c4a7f6625d5d0..e8fe2b3ff11cfdc62a9a075ca89c19ff671f8911 100644 (file)
--- a/src/test/test-fs-util.c
+++ b/src/test/test-fs-util.c
@@ -315,6 +315,32 @@ static void test_dot_or_dot_dot(void) {
         assert_se(!dot_or_dot_dot("..foo"));
 }
 
+static void test_access_fd(void) {
+        _cleanup_(rmdir_and_freep) char *p = NULL;
+        _cleanup_close_ int fd = -1;
+
+        assert_se(mkdtemp_malloc("/tmp/access-fd.XXXXXX", &p) >= 0);
+
+        fd = open(p, O_RDONLY|O_DIRECTORY|O_CLOEXEC);
+        assert_se(fd >= 0);
+
+        assert_se(access_fd(fd, R_OK) >= 0);
+        assert_se(access_fd(fd, F_OK) >= 0);
+        assert_se(access_fd(fd, W_OK) >= 0);
+
+        assert_se(fchmod(fd, 0000) >= 0);
+
+        assert_se(access_fd(fd, F_OK) >= 0);
+
+        if (geteuid() == 0) {
+                assert_se(access_fd(fd, R_OK) >= 0);
+                assert_se(access_fd(fd, W_OK) >= 0);
+        } else {
+                assert_se(access_fd(fd, R_OK) == -EACCES);
+                assert_se(access_fd(fd, W_OK) == -EACCES);
+        }
+}
+
 int main(int argc, char *argv[]) {
         test_unlink_noerrno();
         test_get_files_in_directory();
@@ -322,6 +348,7 @@ int main(int argc, char *argv[]) {
         test_var_tmp();
         test_chase_symlinks();
         test_dot_or_dot_dot();
+        test_access_fd();
 
         return 0;
 }