fs: port privilege checking helpers to 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>

1 files changed, 11 insertions, 9 deletions

diff --git a/fs/inode.c b/fs/inode.c
index 0a86c316937e..03f4eded2a35 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1953,7 +1953,7 @@ EXPORT_SYMBOL(touch_atime);
  * response to write or truncate. Return 0 if nothing has to be changed.
  * Negative value on error (change should be denied).
  */
-int dentry_needs_remove_privs(struct user_namespace *mnt_userns,
+int dentry_needs_remove_privs(struct mnt_idmap *idmap,
 			      struct dentry *dentry)
 {
 	struct inode *inode = d_inode(dentry);
@@ -1963,7 +1963,7 @@ int dentry_needs_remove_privs(struct user_namespace *mnt_userns,
 	if (IS_NOSEC(inode))
 		return 0;
 
-	mask = setattr_should_drop_suidgid(mnt_userns, inode);
+	mask = setattr_should_drop_suidgid(idmap, inode);
 	ret = security_inode_need_killpriv(dentry);
 	if (ret < 0)
 		return ret;
@@ -1995,7 +1995,7 @@ static int __file_remove_privs(struct file *file, unsigned int flags)
 	if (IS_NOSEC(inode) || !S_ISREG(inode->i_mode))
 		return 0;
 
-	kill = dentry_needs_remove_privs(file_mnt_user_ns(file), dentry);
+	kill = dentry_needs_remove_privs(file_mnt_idmap(file), dentry);
 	if (kill < 0)
 		return kill;
 
@@ -2461,7 +2461,7 @@ EXPORT_SYMBOL(current_time);
 
 /**
  * in_group_or_capable - check whether caller is CAP_FSETID privileged
- * @mnt_userns: user namespace of the mount @inode was found from
+ * @idmap:	idmap of the mount @inode was found from
  * @inode:	inode to check
  * @vfsgid:	the new/current vfsgid of @inode
  *
@@ -2471,19 +2471,19 @@ EXPORT_SYMBOL(current_time);
  *
  * Return: true if the caller is sufficiently privileged, false if not.
  */
-bool in_group_or_capable(struct user_namespace *mnt_userns,
+bool in_group_or_capable(struct mnt_idmap *idmap,
 			 const struct inode *inode, vfsgid_t vfsgid)
 {
 	if (vfsgid_in_group_p(vfsgid))
 		return true;
-	if (capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FSETID))
+	if (capable_wrt_inode_uidgid(idmap, inode, CAP_FSETID))
 		return true;
 	return false;
 }
 
 /**
  * mode_strip_sgid - handle the sgid bit for non-directories
- * @mnt_userns: User namespace of the mount the inode was created from
+ * @idmap: idmap of the mount the inode was created from
  * @dir: parent directory inode
  * @mode: mode of the file to be created in @dir
  *
@@ -2495,14 +2495,16 @@ bool in_group_or_capable(struct user_namespace *mnt_userns,
  *
  * Return: the new mode to use for the file
  */
-umode_t mode_strip_sgid(struct user_namespace *mnt_userns,
+umode_t mode_strip_sgid(struct mnt_idmap *idmap,
 			const struct inode *dir, umode_t mode)
 {
+	struct user_namespace *mnt_userns = mnt_idmap_owner(idmap);
+
 	if ((mode & (S_ISGID | S_IXGRP)) != (S_ISGID | S_IXGRP))
 		return mode;
 	if (S_ISDIR(mode) || !dir || !(dir->i_mode & S_ISGID))
 		return mode;
-	if (in_group_or_capable(mnt_userns, dir,
+	if (in_group_or_capable(idmap, dir,
 				i_gid_into_vfsgid(mnt_userns, dir)))
 		return mode;
 	return mode & ~S_ISGID;