[lts9_4] CVE-2025-38498

fs/namespace.c

@@ -2293,6 +2293,19 @@ static int graft_tree(struct mount *mnt, struct mount *p, struct mountpoint *mp)
 	return attach_recursive_mnt(mnt, p, mp, false);
 }
 
+static int may_change_propagation(const struct mount *m)
+{
+        struct mnt_namespace *ns = m->mnt_ns;
+
+	 // it must be mounted in some namespace
+	 if (IS_ERR_OR_NULL(ns))         // is_mounted()
+		 return -EINVAL;
+	 // and the caller must be admin in userns of that namespace
+	 if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN))
+		 return -EPERM;
+	 return 0;
+}
+
 /*
  * Sanity check the flags to change_mnt_propagation.
  */
@@ -2329,6 +2342,10 @@ static int do_change_type(struct path *path, int ms_flags)
 		return -EINVAL;
 
 	namespace_lock();
+	err = may_change_propagation(mnt);
+	if (err)
+		goto out_unlock;
+
 	if (type == MS_SHARED) {
 		err = invent_group_ids(mnt, recurse);
 		if (err)
@@ -2701,6 +2718,71 @@ static bool check_for_nsfs_mounts(struct mount *subtree)
 	return ret;
 }
 
+static int do_set_group(struct path *from_path, struct path *to_path)
+{
+	struct mount *from, *to;
+	int err;
+
+	from = real_mount(from_path->mnt);
+	to = real_mount(to_path->mnt);
+
+	namespace_lock();
+
+	err = may_change_propagation(from);
+	if (err)
+		goto out;
+	err = may_change_propagation(to);
+	if (err)
+		goto out;
+
+	err = -EINVAL;
+	/* To and From paths should be mount roots */
+	if (from_path->dentry != from_path->mnt->mnt_root)
+		goto out;
+	if (to_path->dentry != to_path->mnt->mnt_root)
+		goto out;
+
+	/* Setting sharing groups is only allowed across same superblock */
+	if (from->mnt.mnt_sb != to->mnt.mnt_sb)
+		goto out;
+
+	/* From mount root should be wider than To mount root */
+	if (!is_subdir(to->mnt.mnt_root, from->mnt.mnt_root))
+		goto out;
+
+	/* From mount should not have locked children in place of To's root */
+	if (has_locked_children(from, to->mnt.mnt_root))
+		goto out;
+
+	/* Setting sharing groups is only allowed on private mounts */
+	if (IS_MNT_SHARED(to) || IS_MNT_SLAVE(to))
+		goto out;
+
+	/* From should not be private */
+	if (!IS_MNT_SHARED(from) && !IS_MNT_SLAVE(from))
+		goto out;
+
+	if (IS_MNT_SLAVE(from)) {
+		struct mount *m = from->mnt_master;
+
+		list_add(&to->mnt_slave, &from->mnt_slave);
+		to->mnt_master = m;
+	}
+
+	if (IS_MNT_SHARED(from)) {
+		to->mnt_group_id = from->mnt_group_id;
+		list_add(&to->mnt_share, &from->mnt_share);
+		lock_mount_hash();
+		set_mnt_shared(to);
+		unlock_mount_hash();
+	}
+
+	err = 0;
+out:
+	namespace_unlock();
+	return err;
+}
+
 static int do_move_mount(struct path *old_path, struct path *new_path)
 {
 	struct mnt_namespace *ns;
@@ -3685,7 +3767,10 @@ SYSCALL_DEFINE5(move_mount,
 	if (ret < 0)
 		goto out_to;
 
-	ret = do_move_mount(&from_path, &to_path);
+	if (flags & MOVE_MOUNT_SET_GROUP)
+		ret = do_set_group(&from_path, &to_path);
+	else
+		ret = do_move_mount(&from_path, &to_path);
 
 out_to:
 	path_put(&to_path);

include/uapi/linux/mount.h

@@ -73,7 +73,8 @@
 #define MOVE_MOUNT_T_SYMLINKS		0x00000010 /* Follow symlinks on to path */
 #define MOVE_MOUNT_T_AUTOMOUNTS		0x00000020 /* Follow automounts on to path */
 #define MOVE_MOUNT_T_EMPTY_PATH		0x00000040 /* Empty to path permitted */
-#define MOVE_MOUNT__MASK		0x00000077
+#define MOVE_MOUNT_SET_GROUP		0x00000100 /* Set sharing group instead */
+#define MOVE_MOUNT__MASK		0x00000177
 
 /*
  * fsopen() flags.