Commit bcda7652 authored by Al Viro's avatar Al Viro
Browse files

Allow O_PATH for symlinks 



At that point we can't do almost nothing with them.  They can be opened
with O_PATH, we can manipulate such descriptors with dup(), etc. and
we can see them in /proc/*/{fd,fdinfo}/*.

We can't (and won't be able to) follow /proc/*/fd/* symlinks for those;
there's simply not enough information for pathname resolution to go on
from such point - to resolve a symlink we need to know which directory
does it live in.

We will be able to do useful things with them after the next commit, though -
readlinkat() and fchownat() will be possible to use with dfd being an
O_PATH-opened symlink and empty relative pathname.  Combined with
open_by_handle() it'll give us a way to do realink-by-handle and
lchown-by-handle without messing with more redundant syscalls.

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 1abf0c71

fs/namei.c

+19 −6
Original line number Diff line number Diff line
@@ -766,8 +766,14 @@ __do_follow_link(const struct path *link, struct nameidata *nd, void **p) 
		error = 0;

		if (s)

			error = __vfs_follow_link(nd, s);

		else if (nd->last_type == LAST_BIND)

		else if (nd->last_type == LAST_BIND) {

			nd->flags |= LOOKUP_JUMPED;

			if (nd->path.dentry->d_inode->i_op->follow_link) {

				/* stepped on a _really_ weird one */

				path_put(&nd->path);

				error = -ELOOP;

			}

		}

	}

	return error;

}
@@ -1954,6 +1960,10 @@ static int may_open(struct path *path, int acc_mode, int flag) 
	struct inode *inode = dentry->d_inode;

	int error;



	/* O_PATH? */

	if (!acc_mode)

		return 0;



	if (!inode)

		return -ENOENT;
@@ -2056,7 +2066,7 @@ static struct file *do_last(struct nameidata *nd, struct path *path, 
	int open_flag = op->open_flag;

	int will_truncate = open_flag & O_TRUNC;

	int want_write = 0;

	int skip_perm = 0;

	int acc_mode = op->acc_mode;

	struct file *filp;

	struct inode *inode;

	int error;
@@ -2095,8 +2105,11 @@ static struct file *do_last(struct nameidata *nd, struct path *path, 
	}



	if (!(open_flag & O_CREAT)) {

		int symlink_ok = 0;

		if (nd->last.name[nd->last.len])

			nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;

		if (open_flag & O_PATH && !(nd->flags & LOOKUP_FOLLOW))

			symlink_ok = 1;

		/* we _can_ be in RCU mode here */

		error = do_lookup(nd, &nd->last, path, &inode);

		if (error) {
@@ -2108,7 +2121,7 @@ static struct file *do_last(struct nameidata *nd, struct path *path, 
			terminate_walk(nd);

			return ERR_PTR(-ENOENT);

		}

		if (unlikely(inode->i_op->follow_link)) {

		if (unlikely(inode->i_op->follow_link && !symlink_ok)) {

			/* We drop rcu-walk here */

			if (nameidata_dentry_drop_rcu_maybe(nd, path->dentry))

				return ERR_PTR(-ECHILD);
@@ -2175,7 +2188,7 @@ static struct file *do_last(struct nameidata *nd, struct path *path, 
		/* Don't check for write permission, don't truncate */

		open_flag &= ~O_TRUNC;

		will_truncate = 0;

		skip_perm = 1;

		acc_mode = MAY_OPEN;

		error = security_path_mknod(&nd->path, dentry, mode, 0);

		if (error)

			goto exit_mutex_unlock;
@@ -2225,7 +2238,7 @@ ok: 
		want_write = 1;

	}

common:

	error = may_open(&nd->path, skip_perm ? 0 : op->acc_mode, open_flag);

	error = may_open(&nd->path, acc_mode, open_flag);

	if (error)

		goto exit;

	filp = nameidata_to_filp(nd);
@@ -2358,7 +2371,7 @@ struct file *do_file_open_root(struct dentry *dentry, struct vfsmount *mnt, 


	flags |= LOOKUP_ROOT;



	if (dentry->d_inode->i_op->follow_link)

	if (dentry->d_inode->i_op->follow_link && op->intent & LOOKUP_OPEN)

		return ERR_PTR(-ELOOP);



	file = path_openat(-1, name, &nd, op, flags | LOOKUP_RCU);

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