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: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/namei.c b/fs/namei.c
index e1d9f90..9d4f327 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -766,8 +766,14 @@
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 @@
struct inode *inode = dentry->d_inode;
int error;
+ /* O_PATH? */
+ if (!acc_mode)
+ return 0;
+
if (!inode)
return -ENOENT;
@@ -2056,7 +2066,7 @@
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 @@
}
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 @@
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 @@
/* 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 @@
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 @@
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);