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Subject[PATCH 1/1] readlinkat: ensure we return ENOENT for the empty pathname for normal lookups
Date
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>
---
fs/namei.c | 24 +++++++++++++++++++-----
fs/stat.c | 5 +++--
include/linux/namei.h | 1 +
3 files changed, 23 insertions(+), 7 deletions(-)
diff --git a/fs/namei.c b/fs/namei.c
index 445fd5d..9e013b8 100644
--- 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
@@ -1756,11 +1764,11 @@ 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)) {

@@ -1774,6 +1782,12 @@ 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 9610391..4c814bb 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -296,15 +296,16 @@ 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 76fe2c6..c300127 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -66,6 +66,7 @@ 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)
--
1.7.4.1


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