path_unmount.patch

From 2d514220cd262a772b35fae79358167ae1de9872 Mon Sep 17 00:00:00 2001
From: backslashxx <118538522+backslashxx@users.noreply.github.com>
Date: Sun, 24 Mar 2024 16:02:10 +0800
Subject: [PATCH] BACKPORT: fs/namespace.c path_umount [5.10.9]

---
 fs/internal.h  |  1 +
 fs/namespace.c | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/fs/internal.h b/fs/internal.h
index 204e1e253283..dffebf7b32f3 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -68,6 +68,7 @@ extern int finish_automount(struct vfsmount *, struct path *);
 extern int sb_prepare_remount_readonly(struct super_block *);
 
 extern void __init mnt_init(void);
+int path_umount(struct path *path, int flags);
 
 extern int __mnt_want_write(struct vfsmount *);
 extern int __mnt_want_write_file(struct file *);
diff --git a/fs/namespace.c b/fs/namespace.c
index 6ca275c923c1..0001b8b3aa0a 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1739,6 +1739,39 @@ static inline bool may_mandlock(void)
 }
 #endif
 
+static int can_umount(const struct path *path, int flags)
+{
+	struct mount *mnt = real_mount(path->mnt);
+
+	if (!may_mount())
+		return -EPERM;
+	if (path->dentry != path->mnt->mnt_root)
+		return -EINVAL;
+	if (!check_mnt(mnt))
+		return -EINVAL;
+	if (mnt->mnt.mnt_flags & MNT_LOCKED) /* Check optimistically */
+		return -EINVAL;
+	if (flags & MNT_FORCE && !capable(CAP_SYS_ADMIN))
+		return -EPERM;
+	return 0;
+}
+
+// caller is responsible for flags being sane
+int path_umount(struct path *path, int flags)
+{
+	struct mount *mnt = real_mount(path->mnt);
+	int ret;
+
+	ret = can_umount(path, flags);
+	if (!ret)
+		ret = do_umount(mnt, flags);
+
+	/* we mustn't call path_put() as that would clear mnt_expiry_mark */
+	dput(path->dentry);
+	mntput_no_expire(mnt);
+	return ret;
+}
+
 /*
  * Now umount can handle mount points as well as block devices.
  * This is important for filesystems which use unnamed block devices.