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Merge branch 'work.sane_pwd' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

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Pull misc vfs updates from Al Viro:
 "Making sure that something like a referral point won't end up as pwd
  or root.

  The main part is the last commit (fixing mntns_install()); that one
  fixes a hard-to-hit race. The fchdir() commit is making fchdir(2) a
  bit more robust - it should be impossible to get opened files (even
  O_PATH ones) for referral points in the first place, so the existing
  checks are OK, but checking the same thing as in chdir(2) is just as
  cheap.

  The path_init() commit removes a redundant check that shouldn't have
  been there in the first place"

* 'work.sane_pwd' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  make sure that mntns_install() doesn't end up with referral for root
  path_init(): don't bother with checking MAY_EXEC for LOOKUP_ROOT
  make sure that fchdir() won't accept referral points, etc.
This commit is contained in:
Linus Torvalds
2017-05-12 11:39:59 -07:00
parent e0c4a5fc75 4f757f3cbf
commit 050453295f
4 changed files with 55 additions and 21 deletions
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48
fs/namei.c
View File

@@ -2142,7 +2142,6 @@ OK:
static const char *path_init(struct nameidata *nd, unsigned flags)
{
int retval = 0;
const char *s = nd->name->name;
if (!*s)
@@ -2154,13 +2153,8 @@ static const char *path_init(struct nameidata *nd, unsigned flags)
if (flags & LOOKUP_ROOT) {
struct dentry *root = nd->root.dentry;
struct inode *inode = root->d_inode;
if (*s) {
if (!d_can_lookup(root))
return ERR_PTR(-ENOTDIR);
retval = inode_permission(inode, MAY_EXEC);
if (retval)
return ERR_PTR(retval);
}
if (*s && unlikely(!d_can_lookup(root)))
return ERR_PTR(-ENOTDIR);
nd->path = nd->root;
nd->inode = inode;
if (flags & LOOKUP_RCU) {
@@ -2258,6 +2252,35 @@ static inline int lookup_last(struct nameidata *nd)
return walk_component(nd, 0);
}
static int handle_lookup_down(struct nameidata *nd)
{
struct path path = nd->path;
struct inode *inode = nd->inode;
unsigned seq = nd->seq;
int err;
if (nd->flags & LOOKUP_RCU) {
/*
* don't bother with unlazy_walk on failure - we are
* at the very beginning of walk, so we lose nothing
* if we simply redo everything in non-RCU mode
*/
if (unlikely(!__follow_mount_rcu(nd, &path, &inode, &seq)))
return -ECHILD;
} else {
dget(path.dentry);
err = follow_managed(&path, nd);
if (unlikely(err < 0))
return err;
inode = d_backing_inode(path.dentry);
seq = 0;
}
path_to_nameidata(&path, nd);
nd->inode = inode;
nd->seq = seq;
return 0;
}
/* Returns 0 and nd will be valid on success; Retuns error, otherwise. */
static int path_lookupat(struct nameidata *nd, unsigned flags, struct path *path)
{
@@ -2266,6 +2289,15 @@ static int path_lookupat(struct nameidata *nd, unsigned flags, struct path *path
if (IS_ERR(s))
return PTR_ERR(s);
if (unlikely(flags & LOOKUP_DOWN)) {
err = handle_lookup_down(nd);
if (unlikely(err < 0)) {
terminate_walk(nd);
return err;
}
}
while (!(err = link_path_walk(s, nd))
&& ((err = lookup_last(nd)) > 0)) {
s = trailing_symlink(nd);