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Subject[128/262] readlinkat: ensure we return ENOENT for the empty pathname for normal lookups
3.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Andy Whitcroft <apw@canonical.com>

commit 1fa1e7f615f4d3ae436fa319af6e4eebdd4026a8 upstream.

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 65cfc6722361570bfe255698d9cd4dccaf47570d
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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
fs/namei.c | 18 +++++++++++++-----
fs/stat.c | 5 +++--
include/linux/namei.h | 1 +
3 files changed, 17 insertions(+), 7 deletions(-)

--- a/fs/namei.c
+++ b/fs/namei.c
@@ -136,7 +136,7 @@ static int do_getname(const char __user
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;

@@ -147,6 +147,8 @@ static char *getname_flags(const char __

result = tmp;
if (retval < 0) {
+ if (retval == -ENOENT && empty)
+ *empty = 1;
if (retval != -ENOENT || !(flags & LOOKUP_EMPTY)) {
__putname(tmp);
result = ERR_PTR(retval);
@@ -159,7 +161,7 @@ static char *getname_flags(const char __

char *getname(const char __user * filename)
{
- return getname_flags(filename, 0);
+ return getname_flags(filename, 0, 0);
}

#ifdef CONFIG_AUDITSYSCALL
@@ -1747,11 +1749,11 @@ struct dentry *lookup_one_len(const char
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)) {

@@ -1765,6 +1767,12 @@ int user_path_at(int dfd, const char __u
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)
{
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -296,15 +296,16 @@ SYSCALL_DEFINE4(readlinkat, int, dfd, co
{
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) {
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -67,6 +67,7 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LA
#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)



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