fs: port ->permission() to pass mnt_idmap

Convert to struct mnt_idmap.

Last cycle we merged the necessary infrastructure in
256c8aed2b42 ("fs: introduce dedicated idmap type for mounts").
This is just the conversion to struct mnt_idmap.

Currently we still pass around the plain namespace that was attached to a
mount. This is in general pretty convenient but it makes it easy to
conflate namespaces that are relevant on the filesystem with namespaces
that are relevent on the mount level. Especially for non-vfs developers
without detailed knowledge in this area this can be a potential source for
bugs.

Once the conversion to struct mnt_idmap is done all helpers down to the
really low-level helpers will take a struct mnt_idmap argument instead of
two namespace arguments. This way it becomes impossible to conflate the two
eliminating the possibility of any bugs. All of the vfs and all filesystems
only operate on struct mnt_idmap.

Acked-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>

8 files changed, 24 insertions, 26 deletions

diff --git a/fs/overlayfs/export.c b/fs/overlayfs/export.c
index a25bb3453dde..defd4e231ad2 100644
--- a/fs/overlayfs/export.c
+++ b/fs/overlayfs/export.c
@@ -392,8 +392,8 @@ static struct dentry *ovl_lookup_real_one(struct dentry *connected,
 	 */
 	take_dentry_name_snapshot(&name, real);
 	/*
-	 * No mnt_userns handling here: it's an internal lookup.  Could skip
-	 * permission checking altogether, but for now just use non-mnt_userns
+	 * No idmap handling here: it's an internal lookup.  Could skip
+	 * permission checking altogether, but for now just use non-idmap
 	 * transformed ids.
 	 */
 	this = lookup_one_len(name.name.name, connected, name.name.len);
diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index c9d0c362c7ef..f69d5740c3c4 100644
--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -42,6 +42,7 @@ static struct file *ovl_open_realfile(const struct file *file,
 {
 	struct inode *realinode = d_inode(realpath->dentry);
 	struct inode *inode = file_inode(file);
+	struct mnt_idmap *real_idmap;
 	struct user_namespace *real_mnt_userns;
 	struct file *realfile;
 	const struct cred *old_cred;
@@ -53,8 +54,9 @@ static struct file *ovl_open_realfile(const struct file *file,
 		acc_mode |= MAY_APPEND;
 
 	old_cred = ovl_override_creds(inode->i_sb);
-	real_mnt_userns = mnt_user_ns(realpath->mnt);
-	err = inode_permission(real_mnt_userns, realinode, MAY_OPEN | acc_mode);
+	real_idmap = mnt_idmap(realpath->mnt);
+	real_mnt_userns = mnt_idmap_owner(real_idmap);
+	err = inode_permission(real_idmap, realinode, MAY_OPEN | acc_mode);
 	if (err) {
 		realfile = ERR_PTR(err);
 	} else {
diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index a41a03fcf6bc..d906cf073fba 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -278,7 +278,7 @@ out:
 	return err;
 }
 
-int ovl_permission(struct user_namespace *mnt_userns,
+int ovl_permission(struct mnt_idmap *idmap,
 		   struct inode *inode, int mask)
 {
 	struct inode *upperinode = ovl_inode_upper(inode);
@@ -298,7 +298,7 @@ int ovl_permission(struct user_namespace *mnt_userns,
 	 * Check overlay inode with the creds of task and underlying inode
 	 * with creds of mounter
 	 */
-	err = generic_permission(&init_user_ns, inode, mask);
+	err = generic_permission(&nop_mnt_idmap, inode, mask);
 	if (err)
 		return err;
 
@@ -310,7 +310,7 @@ int ovl_permission(struct user_namespace *mnt_userns,
 		/* Make sure mounter can read file for copy up later */
 		mask |= MAY_READ;
 	}
-	err = inode_permission(mnt_user_ns(realpath.mnt), realinode, mask);
+	err = inode_permission(mnt_idmap(realpath.mnt), realinode, mask);
 	revert_creds(old_cred);
 
 	return err;
@@ -361,7 +361,7 @@ int ovl_xattr_set(struct dentry *dentry, struct inode *inode, const char *name,
 	if (!value && !upperdentry) {
 		ovl_path_lower(dentry, &realpath);
 		old_cred = ovl_override_creds(dentry->d_sb);
-		err = vfs_getxattr(mnt_user_ns(realpath.mnt), realdentry, name, NULL, 0);
+		err = vfs_getxattr(mnt_idmap(realpath.mnt), realdentry, name, NULL, 0);
 		revert_creds(old_cred);
 		if (err < 0)
 			goto out_drop_write;
@@ -403,7 +403,7 @@ int ovl_xattr_get(struct dentry *dentry, struct inode *inode, const char *name,
 
 	ovl_i_path_real(inode, &realpath);
 	old_cred = ovl_override_creds(dentry->d_sb);
-	res = vfs_getxattr(mnt_user_ns(realpath.mnt), realpath.dentry, name, value, size);
+	res = vfs_getxattr(mnt_idmap(realpath.mnt), realpath.dentry, name, value, size);
 	revert_creds(old_cred);
 	return res;
 }
diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index 46753134533a..cfb3420b7df0 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -204,7 +204,7 @@ static struct dentry *ovl_lookup_positive_unlocked(struct ovl_lookup_data *d,
 						   struct dentry *base, int len,
 						   bool drop_negative)
 {
-	struct dentry *ret = lookup_one_unlocked(mnt_user_ns(d->mnt), name, base, len);
+	struct dentry *ret = lookup_one_unlocked(mnt_idmap(d->mnt), name, base, len);
 
 	if (!IS_ERR(ret) && d_flags_negative(smp_load_acquire(&ret->d_flags))) {
 		if (drop_negative && ret->d_lockref.count == 1) {
@@ -711,7 +711,7 @@ struct dentry *ovl_lookup_index(struct ovl_fs *ofs, struct dentry *upper,
 	if (err)
 		return ERR_PTR(err);
 
-	index = lookup_one_positive_unlocked(ovl_upper_mnt_userns(ofs), name.name,
+	index = lookup_one_positive_unlocked(ovl_upper_mnt_idmap(ofs), name.name,
 					     ofs->indexdir, name.len);
 	if (IS_ERR(index)) {
 		err = PTR_ERR(index);
@@ -1182,7 +1182,7 @@ bool ovl_lower_positive(struct dentry *dentry)
 		struct dentry *this;
 		struct dentry *lowerdir = poe->lowerstack[i].dentry;
 
-		this = lookup_one_positive_unlocked(mnt_user_ns(poe->lowerstack[i].layer->mnt),
+		this = lookup_one_positive_unlocked(mnt_idmap(poe->lowerstack[i].layer->mnt),
 						   name->name, lowerdir, name->len);
 		if (IS_ERR(this)) {
 			switch (PTR_ERR(this)) {
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 8091b1914ea3..4d0b278f5630 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -218,7 +218,7 @@ static inline ssize_t ovl_do_getxattr(const struct path *path, const char *name,
 
 	WARN_ON(path->dentry->d_sb != path->mnt->mnt_sb);
 
-	err = vfs_getxattr(mnt_user_ns(path->mnt), path->dentry,
+	err = vfs_getxattr(mnt_idmap(path->mnt), path->dentry,
 			       name, value, size);
 	len = (value && err > 0) ? err : 0;
 
@@ -252,7 +252,7 @@ static inline int ovl_do_setxattr(struct ovl_fs *ofs, struct dentry *dentry,
 				  const char *name, const void *value,
 				  size_t size, int flags)
 {
-	int err = vfs_setxattr(ovl_upper_mnt_userns(ofs), dentry, name,
+	int err = vfs_setxattr(ovl_upper_mnt_idmap(ofs), dentry, name,
 			       value, size, flags);
 
 	pr_debug("setxattr(%pd2, \"%s\", \"%*pE\", %zu, %d) = %i\n",
@@ -270,7 +270,7 @@ static inline int ovl_setxattr(struct ovl_fs *ofs, struct dentry *dentry,
 static inline int ovl_do_removexattr(struct ovl_fs *ofs, struct dentry *dentry,
 				     const char *name)
 {
-	int err = vfs_removexattr(ovl_upper_mnt_userns(ofs), dentry, name);
+	int err = vfs_removexattr(ovl_upper_mnt_idmap(ofs), dentry, name);
 	pr_debug("removexattr(%pd2, \"%s\") = %i\n", dentry, name, err);
 	return err;
 }
@@ -341,7 +341,7 @@ static inline struct dentry *ovl_lookup_upper(struct ovl_fs *ofs,
 					      const char *name,
 					      struct dentry *base, int len)
 {
-	return lookup_one(ovl_upper_mnt_userns(ofs), name, base, len);
+	return lookup_one(ovl_upper_mnt_idmap(ofs), name, base, len);
 }
 
 static inline bool ovl_open_flags_need_copy_up(int flags)
@@ -601,7 +601,7 @@ int ovl_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
 		struct iattr *attr);
 int ovl_getattr(struct mnt_idmap *idmap, const struct path *path,
 		struct kstat *stat, u32 request_mask, unsigned int flags);
-int ovl_permission(struct user_namespace *mnt_userns, struct inode *inode,
+int ovl_permission(struct mnt_idmap *idmap, struct inode *inode,
 		   int mask);
 int ovl_xattr_set(struct dentry *dentry, struct inode *inode, const char *name,
 		  const void *value, size_t size, int flags);
diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
index a6a9235c6168..fd11fe6d6d45 100644
--- a/fs/overlayfs/ovl_entry.h
+++ b/fs/overlayfs/ovl_entry.h
@@ -90,11 +90,6 @@ static inline struct vfsmount *ovl_upper_mnt(struct ovl_fs *ofs)
 	return ofs->layers[0].mnt;
 }
 
-static inline struct user_namespace *ovl_upper_mnt_userns(struct ovl_fs *ofs)
-{
-	return mnt_user_ns(ovl_upper_mnt(ofs));
-}
-
 static inline struct mnt_idmap *ovl_upper_mnt_idmap(struct ovl_fs *ofs)
 {
 	return mnt_idmap(ovl_upper_mnt(ofs));
diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index 8cd2b9947de1..b6952b21a7ee 100644
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -278,7 +278,7 @@ static int ovl_check_whiteouts(const struct path *path, struct ovl_readdir_data
 		while (rdd->first_maybe_whiteout) {
 			p = rdd->first_maybe_whiteout;
 			rdd->first_maybe_whiteout = p->next_maybe_whiteout;
-			dentry = lookup_one(mnt_user_ns(path->mnt), p->name, dir, p->len);
+			dentry = lookup_one(mnt_idmap(path->mnt), p->name, dir, p->len);
 			if (!IS_ERR(dentry)) {
 				p->is_whiteout = ovl_is_whiteout(dentry);
 				dput(dentry);
@@ -480,7 +480,7 @@ static int ovl_cache_update_ino(const struct path *path, struct ovl_cache_entry
 			goto get;
 		}
 	}
-	this = lookup_one(mnt_user_ns(path->mnt), p->name, dir, p->len);
+	this = lookup_one(mnt_idmap(path->mnt), p->name, dir, p->len);
 	if (IS_ERR_OR_NULL(this) || !this->d_inode) {
 		/* Mark a stale entry */
 		p->is_whiteout = true;
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index bde291623c8c..48a3c3fee1b6 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -491,7 +491,8 @@ bool ovl_is_whiteout(struct dentry *dentry)
 struct file *ovl_path_open(const struct path *path, int flags)
 {
 	struct inode *inode = d_inode(path->dentry);
-	struct user_namespace *real_mnt_userns = mnt_user_ns(path->mnt);
+	struct mnt_idmap *real_idmap = mnt_idmap(path->mnt);
+	struct user_namespace *real_mnt_userns = mnt_idmap_owner(real_idmap);
 	int err, acc_mode;
 
 	if (flags & ~(O_ACCMODE | O_LARGEFILE))
@@ -508,7 +509,7 @@ struct file *ovl_path_open(const struct path *path, int flags)
 		BUG();
 	}
 
-	err = inode_permission(real_mnt_userns, inode, acc_mode | MAY_OPEN);
+	err = inode_permission(real_idmap, inode, acc_mode | MAY_OPEN);
 	if (err)
 		return ERR_PTR(err);