https://bugs.gentoo.org/906797
https://github.com/util-linux/util-linux/pull/2248

From 1bd85b64632280d6bf0e86b4ff29da8b19321c5f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Thomas=20Wei=C3=9Fschuh?= <thomas@t-8ch.de>
Date: Sat, 20 May 2023 06:38:20 +0200
Subject: [PATCH] libmount: check for availability of mount_setattr
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

If mount_setattr is not available but needed fall back to the legacy
mount API.

Fixes #2247

Signed-off-by: Thomas Weißschuh <thomas@t-8ch.de>
--- a/libmount/src/hook_mount.c
+++ b/libmount/src/hook_mount.c
@@ -510,6 +510,15 @@ static inline int fsopen_is_supported(void)
 	return rc;
 }
 
+static inline int mount_setattr_is_supported(void)
+{
+	int rc;
+
+	errno = 0;
+	rc = mount_setattr(-1, NULL, 0, NULL, 0);
+	return !(rc == -1 && errno == ENOSYS);
+}
+
 /*
  * open_tree() and fsopen()
  */
@@ -675,9 +684,14 @@ static int hook_prepare(struct libmnt_context *cxt,
 	/* call mount_setattr() */
 	if (!rc
 	    && cxt->helper == NULL
-	    && (set != 0 || clr != 0 || (flags & MS_REMOUNT)))
+	    && (set != 0 || clr != 0 || (flags & MS_REMOUNT))) {
+		if (!mount_setattr_is_supported()) {
+			hookset_deinit(cxt, hs);
+			return 1;
+		}
 		rc = mnt_context_append_hook(cxt, hs, MNT_STAGE_MOUNT, NULL,
 					hook_set_vfsflags);
+	}
 
 	/* call move_mount() to attach target */
 	if (!rc
@@ -688,9 +702,14 @@ static int hook_prepare(struct libmnt_context *cxt,
 					hook_attach_target);
 
 	/* set propagation (has to be attached to VFS) */
-	if (!rc && mnt_optlist_get_propagation(ol))
+	if (!rc && mnt_optlist_get_propagation(ol)) {
+		if (!mount_setattr_is_supported()) {
+			hookset_deinit(cxt, hs);
+			return 1;
+		}
 		rc = mnt_context_append_hook(cxt, hs, MNT_STAGE_MOUNT_POST, NULL,
 					hook_set_propagation);
+	}
 
 	DBG(HOOK, ul_debugobj(hs, "prepare mount done [rc=%d]", rc));
 	return rc;
diff --git a/tests/expected/mount/fallback-mount_setattr b/tests/expected/mount/fallback-mount_setattr
new file mode 100644
index 0000000000..3e18ebf09e
--- /dev/null
+++ b/tests/expected/mount/fallback-mount_setattr
@@ -0,0 +1 @@
+private
--- a/tests/ts/mount/fallback
+++ b/tests/ts/mount/fallback
@@ -68,5 +68,21 @@ $TS_CMD_UMOUNT $MOUNTPOINT
 ts_finalize_subtest
 
 
+ts_init_subtest "mount_setattr"
+"$TS_CMD_MOUNT" "$DEVICE" "$MOUNTPOINT"  >> $TS_OUTPUT 2>> $TS_ERRLOG
+ts_is_mounted $DEVICE || ts_log "Cannot find $DEVICE in /proc/mounts"
+$TS_HELPER_ENOSYS -s mount_setattr -- \
+	"$TS_CMD_MOUNT" -o remount,ro "$MOUNTPOINT" \
+	>> $TS_OUTPUT 2>> $TS_ERRLOG
+$TS_CMD_FINDMNT --kernel --mountpoint "$MOUNTPOINT" --options "ro" &> /dev/null
+[ "$?" == "0" ] || ts_die "Cannot find read-only in $MOUNTPOINT in /proc/self/mountinfo"
+$TS_HELPER_ENOSYS -s mount_setattr -- \
+ 	"$TS_CMD_MOUNT" --make-slave "$MOUNTPOINT" \
+ 	>> $TS_OUTPUT 2>> $TS_ERRLOG
+$TS_CMD_FINDMNT -n --kernel --mountpoint "$MOUNTPOINT" -o PROPAGATION >> $TS_OUTPUT
+$TS_CMD_UMOUNT $MOUNTPOINT
+ts_finalize_subtest
+
+
 ts_finalize