namei: prepare for idmapped mounts

The various vfs_*() helpers are called by filesystems or by the vfs
itself to perform core operations such as create, link, mkdir, mknod, rename,
rmdir, tmpfile and unlink. Enable them to handle idmapped mounts. If the
inode is accessed through an idmapped mount map it into the
mount's user namespace and pass it down. Afterwards the checks and
operations are identical to non-idmapped mounts. If the initial user
namespace is passed nothing changes so non-idmapped mounts will see
identical behavior as before.

Link: https://lore.kernel.org/r/20210121131959.646623-15-christian.brauner@ubuntu.com
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

2 files changed, 13 insertions, 11 deletions

diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index d75c96cb18c3..6904cc2ed7bb 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -821,9 +821,9 @@ static int ovl_remove_upper(struct dentry *dentry, bool is_dir,
 		goto out_dput_upper;
 
 	if (is_dir)
-		err = vfs_rmdir(dir, upper);
+		err = vfs_rmdir(&init_user_ns, dir, upper);
 	else
-		err = vfs_unlink(dir, upper, NULL);
+		err = vfs_unlink(&init_user_ns, dir, upper, NULL);
 	ovl_dir_modified(dentry->d_parent, ovl_type_origin(dentry));
 
 	/*
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 426899681df7..5e9eb46e741a 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -123,7 +123,7 @@ static inline const char *ovl_xattr(struct ovl_fs *ofs, enum ovl_xattr ox)
 
 static inline int ovl_do_rmdir(struct inode *dir, struct dentry *dentry)
 {
-	int err = vfs_rmdir(dir, dentry);
+	int err = vfs_rmdir(&init_user_ns, dir, dentry);
 
 	pr_debug("rmdir(%pd2) = %i\n", dentry, err);
 	return err;
@@ -131,7 +131,7 @@ static inline int ovl_do_rmdir(struct inode *dir, struct dentry *dentry)
 
 static inline int ovl_do_unlink(struct inode *dir, struct dentry *dentry)
 {
-	int err = vfs_unlink(dir, dentry, NULL);
+	int err = vfs_unlink(&init_user_ns, dir, dentry, NULL);
 
 	pr_debug("unlink(%pd2) = %i\n", dentry, err);
 	return err;
@@ -140,7 +140,7 @@ static inline int ovl_do_unlink(struct inode *dir, struct dentry *dentry)
 static inline int ovl_do_link(struct dentry *old_dentry, struct inode *dir,
 			      struct dentry *new_dentry)
 {
-	int err = vfs_link(old_dentry, dir, new_dentry, NULL);
+	int err = vfs_link(old_dentry, &init_user_ns, dir, new_dentry, NULL);
 
 	pr_debug("link(%pd2, %pd2) = %i\n", old_dentry, new_dentry, err);
 	return err;
@@ -149,7 +149,7 @@ static inline int ovl_do_link(struct dentry *old_dentry, struct inode *dir,
 static inline int ovl_do_create(struct inode *dir, struct dentry *dentry,
 				umode_t mode)
 {
-	int err = vfs_create(dir, dentry, mode, true);
+	int err = vfs_create(&init_user_ns, dir, dentry, mode, true);
 
 	pr_debug("create(%pd2, 0%o) = %i\n", dentry, mode, err);
 	return err;
@@ -158,7 +158,7 @@ static inline int ovl_do_create(struct inode *dir, struct dentry *dentry,
 static inline int ovl_do_mkdir(struct inode *dir, struct dentry *dentry,
 			       umode_t mode)
 {
-	int err = vfs_mkdir(dir, dentry, mode);
+	int err = vfs_mkdir(&init_user_ns, dir, dentry, mode);
 	pr_debug("mkdir(%pd2, 0%o) = %i\n", dentry, mode, err);
 	return err;
 }
@@ -166,7 +166,7 @@ static inline int ovl_do_mkdir(struct inode *dir, struct dentry *dentry,
 static inline int ovl_do_mknod(struct inode *dir, struct dentry *dentry,
 			       umode_t mode, dev_t dev)
 {
-	int err = vfs_mknod(dir, dentry, mode, dev);
+	int err = vfs_mknod(&init_user_ns, dir, dentry, mode, dev);
 
 	pr_debug("mknod(%pd2, 0%o, 0%o) = %i\n", dentry, mode, dev, err);
 	return err;
@@ -175,7 +175,7 @@ static inline int ovl_do_mknod(struct inode *dir, struct dentry *dentry,
 static inline int ovl_do_symlink(struct inode *dir, struct dentry *dentry,
 				 const char *oldname)
 {
-	int err = vfs_symlink(dir, dentry, oldname);
+	int err = vfs_symlink(&init_user_ns, dir, dentry, oldname);
 
 	pr_debug("symlink(\"%s\", %pd2) = %i\n", oldname, dentry, err);
 	return err;
@@ -215,8 +215,10 @@ static inline int ovl_do_rename(struct inode *olddir, struct dentry *olddentry,
 {
 	int err;
 	struct renamedata rd = {
+		.old_mnt_userns	= &init_user_ns,
 		.old_dir 	= olddir,
 		.old_dentry 	= olddentry,
+		.new_mnt_userns	= &init_user_ns,
 		.new_dir 	= newdir,
 		.new_dentry 	= newdentry,
 		.flags 		= flags,
@@ -233,14 +235,14 @@ static inline int ovl_do_rename(struct inode *olddir, struct dentry *olddentry,
 
 static inline int ovl_do_whiteout(struct inode *dir, struct dentry *dentry)
 {
-	int err = vfs_whiteout(dir, dentry);
+	int err = vfs_whiteout(&init_user_ns, dir, dentry);
 	pr_debug("whiteout(%pd2) = %i\n", dentry, err);
 	return err;
 }
 
 static inline struct dentry *ovl_do_tmpfile(struct dentry *dentry, umode_t mode)
 {
-	struct dentry *ret = vfs_tmpfile(dentry, mode, 0);
+	struct dentry *ret = vfs_tmpfile(&init_user_ns, dentry, mode, 0);
 	int err = PTR_ERR_OR_ZERO(ret);
 
 	pr_debug("tmpfile(%pd2, 0%o) = %i\n", dentry, mode, err);