From: Al Viro <viro@zeniv.linux.org.uk>
Date: Wed, 2 Jul 2025 05:39:45 +0000 (-0400)
Subject: current_chrooted(): don't bother with follow_down_one()
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=6b6516c56b04d556ce57deab1b8c2833e4af26c6;p=users%2Fhch%2Fmisc.git

current_chrooted(): don't bother with follow_down_one()

All we need here is to follow ->overmount on root mount of namespace...

Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---

diff --git a/fs/namespace.c b/fs/namespace.c
index 6aabf0045389..cf680fbf015e 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -6194,24 +6194,22 @@ bool our_mnt(struct vfsmount *mnt)
 bool current_chrooted(void)
 {
 	/* Does the current process have a non-standard root */
-	struct path ns_root;
+	struct mount *root = current->nsproxy->mnt_ns->root;
 	struct path fs_root;
 	bool chrooted;
 
+	get_fs_root(current->fs, &fs_root);
+
 	/* Find the namespace root */
-	ns_root.mnt = &current->nsproxy->mnt_ns->root->mnt;
-	ns_root.dentry = ns_root.mnt->mnt_root;
-	path_get(&ns_root);
-	while (d_mountpoint(ns_root.dentry) && follow_down_one(&ns_root))
-		;
+	read_seqlock_excl(&mount_lock);
 
-	get_fs_root(current->fs, &fs_root);
+	while (unlikely(root->overmount))
+		root = root->overmount;
 
-	chrooted = !path_equal(&fs_root, &ns_root);
+	chrooted = fs_root.mnt != &root->mnt || !path_mounted(&fs_root);
 
+	read_sequnlock_excl(&mount_lock);
 	path_put(&fs_root);
-	path_put(&ns_root);
-
 	return chrooted;
 }