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Date: Mon, 20 Feb 2023 20:37:53 +0100
From: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
To: mszeredi@...hat.com
Cc: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>,
Al Viro <viro@...iv.linux.org.uk>,
Amir Goldstein <amir73il@...il.com>,
Stéphane Graber <stgraber@...ntu.com>,
Seth Forshee <sforshee@...nel.org>,
Christian Brauner <brauner@...nel.org>,
Andrei Vagin <avagin@...il.com>,
Pavel Tikhomirov <ptikhomirov@...tuozzo.com>,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
criu@...nvz.org
Subject: [RFC PATCH 8/9] namespace: add sb_revalidate_bindmounts helper
Useful if for some reason bindmounts root dentries get invalidated
but it's needed to revalidate existing bindmounts without remounting.
Cc: Miklos Szeredi <mszeredi@...hat.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: Amir Goldstein <amir73il@...il.com>
Cc: Stéphane Graber <stgraber@...ntu.com>
Cc: Seth Forshee <sforshee@...nel.org>
Cc: Christian Brauner <brauner@...nel.org>
Cc: Andrei Vagin <avagin@...il.com>
Cc: Pavel Tikhomirov <ptikhomirov@...tuozzo.com>
Cc: linux-fsdevel@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Cc: criu@...nvz.org
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
---
fs/namespace.c | 90 +++++++++++++++++++++++++++++++++++
include/linux/mnt_namespace.h | 3 ++
2 files changed, 93 insertions(+)
diff --git a/fs/namespace.c b/fs/namespace.c
index ab467ee58341..88491f9c8bbd 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -682,6 +682,96 @@ static int mnt_make_readonly(struct mount *mnt)
return ret;
}
+struct bind_mount_list_item {
+ struct list_head list;
+ struct vfsmount *mnt;
+};
+
+/*
+ * sb_revalidate_bindmounts - Relookup/reset bindmounts root dentries
+ *
+ * Useful if for some reason bindmount root dentries get invalidated
+ * but it's needed to revalidate existing bindmounts without remounting.
+ */
+int sb_revalidate_bindmounts(struct super_block *sb)
+{
+ struct mount *mnt;
+ struct bind_mount_list_item *bmnt, *next;
+ int err = 0;
+ struct vfsmount *root_mnt = NULL;
+ LIST_HEAD(mnt_to_update);
+ char *buf;
+
+ buf = (char *) __get_free_page(GFP_KERNEL);
+ if (!buf)
+ return -ENOMEM;
+
+ lock_mount_hash();
+ list_for_each_entry(mnt, &sb->s_mounts, mnt_instance) {
+ /* we only want to touch bindmounts */
+ if (mnt->mnt.mnt_root == sb->s_root) {
+ if (!root_mnt)
+ root_mnt = mntget(&mnt->mnt);
+
+ continue;
+ }
+
+ bmnt = kzalloc(sizeof(struct bind_mount_list_item), GFP_NOWAIT | __GFP_NOWARN);
+ if (!bmnt) {
+ err = -ENOMEM;
+ goto exit;
+ }
+
+ bmnt->mnt = mntget(&mnt->mnt);
+ list_add_tail(&bmnt->list, &mnt_to_update);
+ }
+ unlock_mount_hash();
+
+ /* TODO: get rid of this limitation */
+ if (!root_mnt) {
+ err = -ENOENT;
+ goto exit;
+ }
+
+ list_for_each_entry_safe(bmnt, next, &mnt_to_update, list) {
+ struct vfsmount *cur_mnt = bmnt->mnt;
+ struct path path;
+ struct dentry *old_root;
+ char *p;
+
+ p = dentry_path(cur_mnt->mnt_root, buf, PAGE_SIZE);
+ if (IS_ERR(p))
+ goto exit;
+
+ /* TODO: are these lookup flags fully safe and correct? */
+ err = vfs_path_lookup(root_mnt->mnt_root, root_mnt,
+ p, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT|LOOKUP_REVAL, &path);
+ if (err)
+ goto exit;
+
+ /* replace bindmount root dentry */
+ lock_mount_hash();
+ old_root = cur_mnt->mnt_root;
+ cur_mnt->mnt_root = dget(path.dentry);
+ dput(old_root);
+ unlock_mount_hash();
+
+ path_put(&path);
+ }
+
+exit:
+ free_page((unsigned long) buf);
+ mntput(root_mnt);
+ list_for_each_entry_safe(bmnt, next, &mnt_to_update, list) {
+ list_del(&bmnt->list);
+ mntput(bmnt->mnt);
+ kfree(bmnt);
+ }
+
+ return err;
+}
+EXPORT_SYMBOL_GPL(sb_revalidate_bindmounts);
+
int sb_prepare_remount_readonly(struct super_block *sb)
{
struct mount *mnt;
diff --git a/include/linux/mnt_namespace.h b/include/linux/mnt_namespace.h
index 8f882f5881e8..20ac29e702f5 100644
--- a/include/linux/mnt_namespace.h
+++ b/include/linux/mnt_namespace.h
@@ -3,6 +3,7 @@
#define _NAMESPACE_H_
#ifdef __KERNEL__
+struct super_block;
struct mnt_namespace;
struct fs_struct;
struct user_namespace;
@@ -13,6 +14,8 @@ extern struct mnt_namespace *copy_mnt_ns(unsigned long, struct mnt_namespace *,
extern void put_mnt_ns(struct mnt_namespace *ns);
extern struct ns_common *from_mnt_ns(struct mnt_namespace *);
+extern int sb_revalidate_bindmounts(struct super_block *sb);
+
extern const struct file_operations proc_mounts_operations;
extern const struct file_operations proc_mountinfo_operations;
extern const struct file_operations proc_mountstats_operations;
--
2.34.1
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