fileio: teach read_one_line_file_at() XAT_FDROOT support

2026-05-11 12:04:02 +02:00
parent 20594fdd6e
commit 1b8a2b6abe
3 changed files with 102 additions and 9 deletions
@@ -420,11 +420,11 @@ int read_one_line_file_at(int dir_fd, const char *filename, char **ret) {
        _cleanup_fclose_ FILE *f = NULL;
        int r;

-        assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
+        assert(dir_fd >= 0 || IN_SET(dir_fd, AT_FDCWD, XAT_FDROOT));
        assert(filename);
        assert(ret);

-        r = fopen_unlocked_at(dir_fd, filename, "re", 0, &f);
+        r = fopen_unlocked_at(dir_fd, filename, "re", /* open_flags= */ 0, &f);
        if (r < 0)
                return r;

@@ -1010,13 +1010,19 @@ static int xfopenat_regular(int dir_fd, const char *path, const char *mode, int

        /* A combination of fopen() with openat() */

-        assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
+        assert(dir_fd >= 0 || IN_SET(dir_fd, AT_FDCWD, XAT_FDROOT));
        assert(mode);
        assert(ret);

        if (dir_fd == AT_FDCWD && path && open_flags == 0)
                f = fopen(path, mode);
-        else {
+        else if (dir_fd == XAT_FDROOT && path && open_flags == 0) {
+                _cleanup_free_ char *j = strjoin("/", path);
+                if (!j)
+                        return -ENOMEM;
+
+                f = fopen(j, mode);
+        } else {
                _cleanup_close_ int fd = -EBADF;
                int mode_flags;

@@ -1051,7 +1057,7 @@ static int xfopenat_unix_socket(int dir_fd, const char *path, const char *bind_n
        FILE *f;
        int r;

-        assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
+        assert(dir_fd >= 0 || IN_SET(dir_fd, AT_FDCWD, XAT_FDROOT));
        assert(ret);

        sk = socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC, 0);
@@ -1099,7 +1105,7 @@ int xfopenat_full(
        FILE *f = NULL;  /* avoid false maybe-uninitialized warning */
        int r;

-        assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
+        assert(dir_fd >= 0 || IN_SET(dir_fd, AT_FDCWD, XAT_FDROOT));
        assert(mode);
        assert(ret);

@@ -1619,13 +1619,17 @@ int connect_unix_path(int fd, int dir_fd, const char *path) {
        _cleanup_close_ int inode_fd = -EBADF;

        assert(fd >= 0);
-        assert(dir_fd == AT_FDCWD || dir_fd >= 0);
+        assert(IN_SET(dir_fd, AT_FDCWD, XAT_FDROOT) || dir_fd >= 0);

        /* Connects to the specified AF_UNIX socket in the file system. Works around the 108 byte size limit
         * in sockaddr_un, by going via O_PATH if needed. This hence works for any kind of path. */

-        if (!path)
+        if (!path) {
+                if (dir_fd < 0)
+                        return -EISDIR;
+
                return connect_unix_inode(fd, dir_fd); /* If no path is specified, then dir_fd refers to the socket inode to connect to. */
+        }

        /* Refuse zero length path early, to make sure AF_UNIX stack won't mistake this for an abstract
         * namespace path, since first char is NUL */
@@ -1640,7 +1644,14 @@ int connect_unix_path(int fd, int dir_fd, const char *path) {
         * exist. If the path is too long, we also need to take the indirect route, since we can't fit this
         * into a sockaddr_un directly. */

-        inode_fd = openat(dir_fd, path, O_PATH|O_CLOEXEC);
+        if (dir_fd == XAT_FDROOT) {
+                _cleanup_free_ char *j = strjoin("/", path);
+                if (!j)
+                        return -ENOMEM;
+
+                inode_fd = open(j, O_PATH|O_CLOEXEC);
+        } else
+                inode_fd = openat(dir_fd, path, O_PATH|O_CLOEXEC);
        if (inode_fd < 0)
                return -errno;

@@ -747,4 +747,80 @@ TEST(write_data_file_atomic_at) {
        ASSERT_OK_ERRNO(rmdir("/tmp/zzz"));
 }

+TEST(read_one_line_file_at_xat_fdroot) {
+        _cleanup_(rm_rf_physical_and_freep) char *t = NULL;
+        _cleanup_free_ char *fn = NULL, *buf = NULL;
+
+        ASSERT_OK(mkdtemp_malloc("/tmp/test-r1lf-xatfd-XXXXXX", &t));
+        ASSERT_TRUE(path_is_absolute(t));
+
+        ASSERT_NOT_NULL(fn = path_join(t, "hello"));
+        ASSERT_OK(write_string_file(fn, "first line\nsecond line", WRITE_STRING_FILE_CREATE));
+
+        /* XAT_FDROOT is supposed to root the path at the host's "/"; the implementation prepends a "/" so
+         * we pass the path without leading slash. */
+        ASSERT_OK_EQ(read_one_line_file_at(XAT_FDROOT, fn + 1, &buf), (int) STRLEN("first line\n"));
+        ASSERT_STREQ(buf, "first line");
+        buf = mfree(buf);
+
+        /* Sanity check: AT_FDCWD with the absolute path gives the same result. */
+        ASSERT_OK_EQ(read_one_line_file_at(AT_FDCWD, fn, &buf), (int) STRLEN("first line\n"));
+        ASSERT_STREQ(buf, "first line");
+        buf = mfree(buf);
+
+        /* /proc/version should always be readable via XAT_FDROOT (some build envs may restrict it; tolerate
+         * that). */
+        int r = read_one_line_file_at(XAT_FDROOT, "proc/version", &buf);
+        if (!ERRNO_IS_NEG_PRIVILEGE(r)) {
+                ASSERT_OK(r);
+                ASSERT_FALSE(isempty(buf));
+                buf = mfree(buf);
+        }
+
+        /* Non-existent path through XAT_FDROOT should yield -ENOENT. */
+        ASSERT_ERROR(read_one_line_file_at(XAT_FDROOT, "tmp/this/path/really/should/not/exist", &buf), ENOENT);
+
+        /* Now create a Unix socket in the same temp dir, and verify that read_one_line_file_at() returns
+         * -ENXIO when pointed at it via XAT_FDROOT — read_one_line_file_at() does not enable the socket
+         * fallback. */
+        _cleanup_free_ char *sockpath = NULL;
+        ASSERT_NOT_NULL(sockpath = path_join(t, "socket"));
+
+        _cleanup_close_ int listener = -EBADF;
+        ASSERT_OK(listener = socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC, /* protocol= */ 0));
+
+        union sockaddr_union sa;
+        ASSERT_OK(sockaddr_un_set_path(&sa.un, sockpath));
+        ASSERT_OK_ERRNO(bind(listener, &sa.sa, sockaddr_un_len(&sa.un)));
+        ASSERT_OK_ERRNO(listen(listener, 1));
+
+        ASSERT_ERROR(read_one_line_file_at(XAT_FDROOT, sockpath + 1, &buf), ENXIO);
+
+        /* But read_full_file_full() with READ_FULL_FILE_CONNECT_SOCKET *does* enable the socket fallback,
+         * which routes through xfopenat_unix_socket() and connect_unix_path() — both now teach the
+         * XAT_FDROOT codepath. Use that to exercise the socket open via XAT_FDROOT. */
+        static const char test_sock_str[] = "hello via xat_fdroot socket\n";
+
+        _cleanup_(pidref_done) PidRef pidref = PIDREF_NULL;
+        int pr = ASSERT_OK(pidref_safe_fork("(server)", FORK_DEATHSIG_SIGTERM|FORK_LOG, &pidref));
+        if (pr == 0) {
+                _cleanup_close_ int rfd = -EBADF;
+                ASSERT_OK(rfd = accept4(listener, /* addr= */ NULL, /* addrlen= */ NULL, SOCK_CLOEXEC));
+                ASSERT_OK_EQ_ERRNO(write(rfd, test_sock_str, sizeof(test_sock_str) - 1),
+                                   (ssize_t) sizeof(test_sock_str) - 1);
+                _exit(EXIT_SUCCESS);
+        }
+
+        _cleanup_free_ char *data = NULL;
+        size_t size;
+        ASSERT_OK(read_full_file_full(XAT_FDROOT, sockpath + 1,
+                                      /* offset= */ UINT64_MAX, /* size= */ SIZE_MAX,
+                                      READ_FULL_FILE_CONNECT_SOCKET, /* bind_name= */ NULL,
+                                      &data, &size));
+        ASSERT_EQ(size, sizeof(test_sock_str) - 1);
+        ASSERT_STREQ(data, test_sock_str);
+
+        ASSERT_OK(pidref_wait_for_terminate_and_check("(server)", &pidref, WAIT_LOG));
+}
+
 DEFINE_TEST_MAIN(LOG_DEBUG);