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readlinkat: ensure we return ENOENT for the empty pathname for normal lookups

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Since the commit below which added O_PATH support to the *at() calls, the
error return for readlink/readlinkat for the empty pathname has switched
from ENOENT to EINVAL:

  commit 65cfc67223
  Author: Al Viro <[email protected]>
  Date:   Sun Mar 13 15:56:26 2011 -0400

    readlinkat(), fchownat() and fstatat() with empty relative pathnames

This is both unexpected for userspace and makes readlink/readlinkat
inconsistant with all other interfaces; and inconsistant with our stated
return for these pathnames.

As the readlinkat call does not have a flags parameter we cannot use the
AT_EMPTY_PATH approach used in the other calls.  Therefore expose whether
the original path is infact entry via a new user_path_at_empty() path
lookup function.  Use this to determine whether to default to EINVAL or
ENOENT for failures.

Addresses http://bugs.launchpad.net/bugs/817187

[[email protected]: remove unused getname_flags()]
Signed-off-by: Andy Whitcroft <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Al Viro <[email protected]>
Cc: <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>
This commit is contained in:
Andy Whitcroft 2011-11-02 09:44:39 +01:00 • committed by Christoph Hellwig
commit 1fa1e7f615
3 changed files with 17 additions and 7 deletions
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5
fs/stat.c
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@ -294,15 +294,16 @@ SYSCALL_DEFINE4(readlinkat, int, dfd, const char __user *, pathname,
{
struct path path;
int error;
int empty = 0;
if (bufsiz <= 0)
return -EINVAL;
error = user_path_at(dfd, pathname, LOOKUP_EMPTY, &path);
error = user_path_at_empty(dfd, pathname, LOOKUP_EMPTY, &path, &empty);
if (!error) {
struct inode *inode = path.dentry->d_inode;
error = -EINVAL;
error = empty ? -ENOENT : -EINVAL;
if (inode->i_op->readlink) {
error = security_inode_readlink(path.dentry);
if (!error) {