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Allow O_PATH for symlinks

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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: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2011-03-13 16:42:14 -04:00
parent 1abf0c718f
commit bcda76524c
1 changed files with 19 additions and 6 deletions
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25
fs/namei.c
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@ -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 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
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);