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

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.

BugLink: http://bugs.launchpad.net/bugs/817187
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/fs/namei.c b/fs/namei.c
index 0b3138de2a3b79fd8d1bf1843e405506f343f605..28b440c2cb4beac8cd9a526555c1dd1572cf347e 100644 (file)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -137,7 +137,8 @@ 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_empty(const char __user * filename,
+                                                       int flags, int *empty)
 {
        char *tmp, *result;
 
@@ -148,6 +149,8 @@ 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);
@@ -158,9 +161,14 @@ static char *getname_flags(const char __user * filename, int flags)
        return result;
 }
 
+static char *getname_flags(const char __user * filename, int flags)
+{
+       return getname_flags_empty(filename, flags, 0);
+}
+
 char *getname(const char __user * filename)
 {
-       return getname_flags(filename, 0);
+       return getname_flags_empty(filename, 0, 0);
 }
 
 #ifdef CONFIG_AUDITSYSCALL
@@ -1798,11 +1806,11 @@ 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_empty(name, flags, empty);
        int err = PTR_ERR(tmp);
        if (!IS_ERR(tmp)) {
 
@@ -1816,6 +1824,12 @@ 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)
 {

diff --git a/fs/stat.c b/fs/stat.c
index 78a3aa83c7eac3f153cc5e370cabd754babb9aab..9ef37a58eef4c9829e2709a4f21b9b25651cd904 100644 (file)
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -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) {

diff --git a/include/linux/namei.h b/include/linux/namei.h
index 409328d1cbbb31d5173fc197154ca48c00b0492d..ffc02135c483c2c6363eed8dc0a4b15b2def6656 100644 (file)
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -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)