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, 16 insertions, 22 deletions

diff --git a/fs/namei.c b/fs/namei.c
index 48dd44251dda..ed9e877f72c7 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -398,7 +398,6 @@ int generic_permission(struct mnt_idmap *idmap, struct inode *inode,
 		       int mask)
 {
 	int ret;
-	struct user_namespace *mnt_userns = mnt_idmap_owner(idmap);
 
 	/*
 	 * Do the basic permission checks.
@@ -410,10 +409,10 @@ int generic_permission(struct mnt_idmap *idmap, struct inode *inode,
 	if (S_ISDIR(inode->i_mode)) {
 		/* DACs are overridable for directories */
 		if (!(mask & MAY_WRITE))
-			if (capable_wrt_inode_uidgid(mnt_userns, inode,
+			if (capable_wrt_inode_uidgid(idmap, inode,
 						     CAP_DAC_READ_SEARCH))
 				return 0;
-		if (capable_wrt_inode_uidgid(mnt_userns, inode,
+		if (capable_wrt_inode_uidgid(idmap, inode,
 					     CAP_DAC_OVERRIDE))
 			return 0;
 		return -EACCES;
@@ -424,7 +423,7 @@ int generic_permission(struct mnt_idmap *idmap, struct inode *inode,
 	 */
 	mask &= MAY_READ | MAY_WRITE | MAY_EXEC;
 	if (mask == MAY_READ)
-		if (capable_wrt_inode_uidgid(mnt_userns, inode,
+		if (capable_wrt_inode_uidgid(idmap, inode,
 					     CAP_DAC_READ_SEARCH))
 			return 0;
 	/*
@@ -433,7 +432,7 @@ int generic_permission(struct mnt_idmap *idmap, struct inode *inode,
 	 * at least one exec bit set.
 	 */
 	if (!(mask & MAY_EXEC) || (inode->i_mode & S_IXUGO))
-		if (capable_wrt_inode_uidgid(mnt_userns, inode,
+		if (capable_wrt_inode_uidgid(idmap, inode,
 					     CAP_DAC_OVERRIDE))
 			return 0;
 
@@ -2885,16 +2884,17 @@ int user_path_at_empty(int dfd, const char __user *name, unsigned flags,
 }
 EXPORT_SYMBOL(user_path_at_empty);
 
-int __check_sticky(struct user_namespace *mnt_userns, struct inode *dir,
+int __check_sticky(struct mnt_idmap *idmap, struct inode *dir,
 		   struct inode *inode)
 {
 	kuid_t fsuid = current_fsuid();
+	struct user_namespace *mnt_userns = mnt_idmap_owner(idmap);
 
 	if (vfsuid_eq_kuid(i_uid_into_vfsuid(mnt_userns, inode), fsuid))
 		return 0;
 	if (vfsuid_eq_kuid(i_uid_into_vfsuid(mnt_userns, dir), fsuid))
 		return 0;
-	return !capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FOWNER);
+	return !capable_wrt_inode_uidgid(idmap, inode, CAP_FOWNER);
 }
 EXPORT_SYMBOL(__check_sticky);
 
@@ -2944,7 +2944,7 @@ static int may_delete(struct mnt_idmap *idmap, struct inode *dir,
 	if (IS_APPEND(dir))
 		return -EPERM;
 
-	if (check_sticky(mnt_userns, dir, inode) || IS_APPEND(inode) ||
+	if (check_sticky(idmap, dir, inode) || IS_APPEND(inode) ||
 	    IS_IMMUTABLE(inode) || IS_SWAPFILE(inode) ||
 	    HAS_UNMAPPED_ID(idmap, inode))
 		return -EPERM;
@@ -3050,7 +3050,7 @@ static inline umode_t mode_strip_umask(const struct inode *dir, umode_t mode)
 
 /**
  * vfs_prepare_mode - prepare the mode to be used for a new inode
- * @mnt_userns:		user namespace of the mount the inode was found from
+ * @idmap:	idmap of the mount the inode was found from
  * @dir:	parent directory of the new inode
  * @mode:	mode of the new inode
  * @mask_perms:	allowed permission by the vfs
@@ -3071,11 +3071,11 @@ static inline umode_t mode_strip_umask(const struct inode *dir, umode_t mode)
  *
  * Returns: mode to be passed to the filesystem
  */
-static inline umode_t vfs_prepare_mode(struct user_namespace *mnt_userns,
+static inline umode_t vfs_prepare_mode(struct mnt_idmap *idmap,
 				       const struct inode *dir, umode_t mode,
 				       umode_t mask_perms, umode_t type)
 {
-	mode = mode_strip_sgid(mnt_userns, dir, mode);
+	mode = mode_strip_sgid(idmap, dir, mode);
 	mode = mode_strip_umask(dir, mode);
 
 	/*
@@ -3107,7 +3107,6 @@ static inline umode_t vfs_prepare_mode(struct user_namespace *mnt_userns,
 int vfs_create(struct mnt_idmap *idmap, struct inode *dir,
 	       struct dentry *dentry, umode_t mode, bool want_excl)
 {
-	struct user_namespace *mnt_userns = mnt_idmap_owner(idmap);
 	int error;
 
 	error = may_create(idmap, dir, dentry);
@@ -3117,7 +3116,7 @@ int vfs_create(struct mnt_idmap *idmap, struct inode *dir,
 	if (!dir->i_op->create)
 		return -EACCES;	/* shouldn't it be ENOSYS? */
 
-	mode = vfs_prepare_mode(mnt_userns, dir, mode, S_IALLUGO, S_IFREG);
+	mode = vfs_prepare_mode(idmap, dir, mode, S_IALLUGO, S_IFREG);
 	error = security_inode_create(dir, dentry, mode);
 	if (error)
 		return error;
@@ -3329,7 +3328,6 @@ static struct dentry *lookup_open(struct nameidata *nd, struct file *file,
 				  bool got_write)
 {
 	struct mnt_idmap *idmap;
-	struct user_namespace *mnt_userns;
 	struct dentry *dir = nd->path.dentry;
 	struct inode *dir_inode = dir->d_inode;
 	int open_flag = op->open_flag;
@@ -3378,11 +3376,10 @@ static struct dentry *lookup_open(struct nameidata *nd, struct file *file,
 	if (unlikely(!got_write))
 		open_flag &= ~O_TRUNC;
 	idmap = mnt_idmap(nd->path.mnt);
-	mnt_userns = mnt_idmap_owner(idmap);
 	if (open_flag & O_CREAT) {
 		if (open_flag & O_EXCL)
 			open_flag &= ~O_TRUNC;
-		mode = vfs_prepare_mode(mnt_userns, dir->d_inode, mode, mode, mode);
+		mode = vfs_prepare_mode(idmap, dir->d_inode, mode, mode, mode);
 		if (likely(got_write))
 			create_error = may_o_create(idmap, &nd->path,
 						    dentry, mode);
@@ -3600,7 +3597,6 @@ static int vfs_tmpfile(struct mnt_idmap *idmap,
 		       const struct path *parentpath,
 		       struct file *file, umode_t mode)
 {
-	struct user_namespace *mnt_userns = mnt_idmap_owner(idmap);
 	struct dentry *child;
 	struct inode *dir = d_inode(parentpath->dentry);
 	struct inode *inode;
@@ -3618,7 +3614,7 @@ static int vfs_tmpfile(struct mnt_idmap *idmap,
 		return -ENOMEM;
 	file->f_path.mnt = parentpath->mnt;
 	file->f_path.dentry = child;
-	mode = vfs_prepare_mode(mnt_userns, dir, mode, mode, mode);
+	mode = vfs_prepare_mode(idmap, dir, mode, mode, mode);
 	error = dir->i_op->tmpfile(idmap, dir, file, mode);
 	dput(child);
 	if (error)
@@ -3902,7 +3898,6 @@ EXPORT_SYMBOL(user_path_create);
 int vfs_mknod(struct mnt_idmap *idmap, struct inode *dir,
 	      struct dentry *dentry, umode_t mode, dev_t dev)
 {
-	struct user_namespace *mnt_userns = mnt_idmap_owner(idmap);
 	bool is_whiteout = S_ISCHR(mode) && dev == WHITEOUT_DEV;
 	int error = may_create(idmap, dir, dentry);
 
@@ -3916,7 +3911,7 @@ int vfs_mknod(struct mnt_idmap *idmap, struct inode *dir,
 	if (!dir->i_op->mknod)
 		return -EPERM;
 
-	mode = vfs_prepare_mode(mnt_userns, dir, mode, mode, mode);
+	mode = vfs_prepare_mode(idmap, dir, mode, mode, mode);
 	error = devcgroup_inode_mknod(mode, dev);
 	if (error)
 		return error;
@@ -4029,7 +4024,6 @@ SYSCALL_DEFINE3(mknod, const char __user *, filename, umode_t, mode, unsigned, d
 int vfs_mkdir(struct mnt_idmap *idmap, struct inode *dir,
 	      struct dentry *dentry, umode_t mode)
 {
-	struct user_namespace *mnt_userns = mnt_idmap_owner(idmap);
 	int error;
 	unsigned max_links = dir->i_sb->s_max_links;
 
@@ -4040,7 +4034,7 @@ int vfs_mkdir(struct mnt_idmap *idmap, struct inode *dir,
 	if (!dir->i_op->mkdir)
 		return -EPERM;
 
-	mode = vfs_prepare_mode(mnt_userns, dir, mode, S_IRWXUGO | S_ISVTX, 0);
+	mode = vfs_prepare_mode(idmap, dir, mode, S_IRWXUGO | S_ISVTX, 0);
 	error = security_inode_mkdir(dir, dentry, mode);
 	if (error)
 		return error;