fileio: port read_file_full() to use connect_unix_path()

This way we can connect correctly to any AF_UNIX socket in the file
system, and even save some code. Yay!

This also adds some test code for this, that ensures read_file_full()
works correctly for AF_UNIX sockets that violate the 108 char limit.

Supporting sockets like this kinda matters I think, for the simple
reason that apps want to build socket paths via XDG_RUNTIME_DIR and
suchlike, and we should be able to connect to them, even via
non-normalized paths.

1 files changed, 6 insertions, 21 deletions

diff --git a/src/basic/fileio.c b/src/basic/fileio.c
index c2497ff856..2c4ba89a15 100644
--- a/src/basic/fileio.c
+++ b/src/basic/fileio.c
@@ -763,8 +763,7 @@ int read_full_file_full(
 
         r = xfopenat(dir_fd, filename, "re", 0, &f);
         if (r < 0) {
-                _cleanup_close_ int dfd = -1, sk = -1;
-                union sockaddr_union sa;
+                _cleanup_close_ int sk = -1;
 
                 /* ENXIO is what Linux returns if we open a node that is an AF_UNIX socket */
                 if (r != -ENXIO)
@@ -778,22 +777,6 @@ int read_full_file_full(
                 if (offset != UINT64_MAX)
                         return -ENXIO;
 
-                if (dir_fd == AT_FDCWD)
-                        r = sockaddr_un_set_path(&sa.un, filename);
-                else {
-                        /* If we shall operate relative to some directory, then let's use O_PATH first to
-                         * open the socket inode, and then connect to it via /proc/self/fd/. We have to do
-                         * this since there's not connectat() that takes a directory fd as first arg. */
-
-                        dfd = openat(dir_fd, filename, O_PATH|O_CLOEXEC);
-                        if (dfd < 0)
-                                return -errno;
-
-                        r = sockaddr_un_set_path(&sa.un, FORMAT_PROC_FD_PATH(dfd));
-                }
-                if (r < 0)
-                        return r;
-
                 sk = socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC, 0);
                 if (sk < 0)
                         return -errno;
@@ -812,9 +795,11 @@ int read_full_file_full(
                                 return -errno;
                 }
 
-                if (connect(sk, &sa.sa, SOCKADDR_UN_LEN(sa.un)) < 0)
-                        return errno == ENOTSOCK ? -ENXIO : -errno; /* propagate original error if this is
-                                                                     * not a socket after all */
+                r = connect_unix_path(sk, dir_fd, filename);
+                if (IN_SET(r, -ENOTSOCK, -EINVAL)) /* propagate original error if this is not a socket after all */
+                        return -ENXIO;
+                if (r < 0)
+                        return r;
 
                 if (shutdown(sk, SHUT_WR) < 0)
                         return -errno;