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Commit 1fa1e7f6 authored by Andy Whitcroft's avatar Andy Whitcroft Committed by Christoph Hellwig
Browse files

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 65cfc672
  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: default avatarAndy 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
parent 32096ea1

fs/namei.c

+13 −5
Original line number Diff line number Diff line
@@ -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)

{

fs/stat.c

+3 −2
Original line number Diff line number Diff line
@@ -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) {

include/linux/namei.h

+1 −0
Original line number Diff line number Diff line
@@ -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)