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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 <viro@zeniv.linux.org.uk>
  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

[akpm@linux-foundation.org: remove unused getname_flags()]
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: <stable@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
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
Download patch file Download diff file Expand all files Collapse all files

18
fs/namei.c
View file

@ -137,7 +137,7 @@ static int do_getname(const char __user *filename, char *page)
return retval;
}
static char *getname_flags(const char __user * filename, int flags)
static char *getname_flags(const char __user *filename, int flags, int *empty)
{
char *tmp, *result;
@ -148,6 +148,8 @@ static char *getname_flags(const char __user * filename, int flags)
result = tmp;
if (retval < 0) {
if (retval == -ENOENT && empty)
*empty = 1;
if (retval != -ENOENT || !(flags & LOOKUP_EMPTY)) {
__putname(tmp);
result = ERR_PTR(retval);
@ -160,7 +162,7 @@ static char *getname_flags(const char __user * filename, int flags)
char *getname(const char __user * filename)
{
return getname_flags(filename, 0);
return getname_flags(filename, 0, 0);
}
#ifdef CONFIG_AUDITSYSCALL
@ -1798,11 +1800,11 @@ struct dentry *lookup_one_len(const char *name, struct dentry *base, int len)
return __lookup_hash(&this, base, NULL);
}
int user_path_at(int dfd, const char __user *name, unsigned flags,
struct path *path)
int user_path_at_empty(int dfd, const char __user *name, unsigned flags,
struct path *path, int *empty)
{
struct nameidata nd;
char *tmp = getname_flags(name, flags);
char *tmp = getname_flags(name, flags, empty);
int err = PTR_ERR(tmp);
if (!IS_ERR(tmp)) {
@ -1816,6 +1818,12 @@ int user_path_at(int dfd, const char __user *name, unsigned flags,
return err;
}
int user_path_at(int dfd, const char __user *name, unsigned flags,
struct path *path)
{
return user_path_at_empty(dfd, name, flags, path, 0);
}
static int user_path_parent(int dfd, const char __user *path,
struct nameidata *nd, char **name)
{

5
fs/stat.c
View file

@ -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) {

1
include/linux/namei.h
View file

@ -67,6 +67,7 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT, LAST_BIND};
#define LOOKUP_EMPTY 0x4000
extern int user_path_at(int, const char __user *, unsigned, struct path *);
extern int user_path_at_empty(int, const char __user *, unsigned, struct path *, int *empty);
#define user_path(name, path) user_path_at(AT_FDCWD, name, LOOKUP_FOLLOW, path)
#define user_lpath(name, path) user_path_at(AT_FDCWD, name, 0, path)