util: rework fgetxattrat_fake() to use O_PATH

That way, we don't ever open the file, thus leave the atime untouched,
and this works even when unprivileged.

2 files changed, 40 insertions, 2 deletions

diff --git a/src/basic/util.c b/src/basic/util.c
index c63ec0ceb0..9f520462cf 100644
--- a/src/basic/util.c
+++ b/src/basic/util.c
@@ -6168,16 +6168,19 @@ int openpt_in_namespace(pid_t pid, int flags) {
 }
 
 ssize_t fgetxattrat_fake(int dirfd, const char *filename, const char *attribute, void *value, size_t size, int flags) {
+        char fn[strlen("/proc/self/fd/") + DECIMAL_STR_MAX(int) + 1];
         _cleanup_close_ int fd = -1;
         ssize_t l;
 
         /* The kernel doesn't have a fgetxattrat() command, hence let's emulate one */
 
-        fd = openat(dirfd, filename, O_RDONLY|O_CLOEXEC|O_NOCTTY|O_NOATIME|(flags & AT_SYMLINK_NOFOLLOW ? O_NOFOLLOW : 0));
+        fd = openat(dirfd, filename, O_RDONLY|O_CLOEXEC|O_NOCTTY|O_PATH|(flags & AT_SYMLINK_NOFOLLOW ? O_NOFOLLOW : 0));
         if (fd < 0)
                 return -errno;
 
-        l = fgetxattr(fd, attribute, value, size);
+        xsprintf(fn, "/proc/self/fd/%i", fd);
+
+        l = getxattr(fn, attribute, value, size);
         if (l < 0)
                 return -errno;
 
diff --git a/src/test/test-util.c b/src/test/test-util.c
index 7de1535fb6..503e840803 100644
--- a/src/test/test-util.c
+++ b/src/test/test-util.c
@@ -26,7 +26,9 @@
 #include <math.h>
 #include <signal.h>
 #include <string.h>
+#include <sys/types.h>
 #include <sys/wait.h>
+#include <sys/xattr.h>
 #include <unistd.h>
 
 #include "conf-parser.h"
@@ -2263,6 +2265,38 @@ static void test_strcmp_ptr(void) {
         assert_se(strcmp_ptr("", "") == 0);
 }
 
+static void test_fgetxattrat_fake(void) {
+        char t[] = "/var/tmp/xattrtestXXXXXX";
+        _cleanup_close_ int fd = -1;
+        const char *x;
+        char v[3] = {};
+        int r;
+
+        assert_se(mkdtemp(t));
+        x = strjoina(t, "/test");
+        assert_se(touch(x) >= 0);
+
+        r = setxattr(x, "user.foo", "bar", 3, 0);
+        if (r < 0 && errno == EOPNOTSUPP) /* no xattrs supported on /var/tmp... */
+                goto cleanup;
+        assert_se(r >= 0);
+
+        fd = open(t, O_RDONLY|O_DIRECTORY|O_CLOEXEC|O_NOCTTY);
+        assert_se(fd >= 0);
+
+        assert_se(fgetxattrat_fake(fd, "test", "user.foo", v, 3, 0) >= 0);
+        assert_se(memcmp(v, "bar", 3) == 0);
+
+        safe_close(fd);
+        fd = open("/", O_RDONLY|O_DIRECTORY|O_CLOEXEC|O_NOCTTY);
+        assert_se(fd >= 0);
+        assert_se(fgetxattrat_fake(fd, "usr", "user.idontexist", v, 3, 0) == -ENODATA);
+
+cleanup:
+        assert_se(unlink(x) >= 0);
+        assert_se(rmdir(t) >= 0);
+}
+
 int main(int argc, char *argv[]) {
         log_parse_environment();
         log_open();
@@ -2353,6 +2387,7 @@ int main(int argc, char *argv[]) {
         test_parse_mode();
         test_tempfn();
         test_strcmp_ptr();
+        test_fgetxattrat_fake();
 
         return 0;
 }