make sure that mntns_install() doesn't end up with referral for root
new flag: LOOKUP_DOWN. If the starting point is overmounted, cross
into whatever's mounted on top, triggering referrals et.al.
Use that instead of follow_down_one() loop in mntns_install(), handle
errors properly.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/namei.c b/fs/namei.c
index 60c0a78..646db9cf 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2252,6 +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)
{
@@ -2260,6 +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);
diff --git a/fs/namespace.c b/fs/namespace.c
index cc1375ef..0886ef2 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3465,8 +3465,9 @@ static void mntns_put(struct ns_common *ns)
static int mntns_install(struct nsproxy *nsproxy, struct ns_common *ns)
{
struct fs_struct *fs = current->fs;
- struct mnt_namespace *mnt_ns = to_mnt_ns(ns);
+ struct mnt_namespace *mnt_ns = to_mnt_ns(ns), *old_mnt_ns;
struct path root;
+ int err;
if (!ns_capable(mnt_ns->user_ns, CAP_SYS_ADMIN) ||
!ns_capable(current_user_ns(), CAP_SYS_CHROOT) ||
@@ -3477,15 +3478,18 @@ static int mntns_install(struct nsproxy *nsproxy, struct ns_common *ns)
return -EINVAL;
get_mnt_ns(mnt_ns);
- put_mnt_ns(nsproxy->mnt_ns);
+ old_mnt_ns = nsproxy->mnt_ns;
nsproxy->mnt_ns = mnt_ns;
/* Find the root */
- root.mnt = &mnt_ns->root->mnt;
- root.dentry = mnt_ns->root->mnt.mnt_root;
- path_get(&root);
- while(d_mountpoint(root.dentry) && follow_down_one(&root))
- ;
+ err = vfs_path_lookup(mnt_ns->root->mnt.mnt_root, &mnt_ns->root->mnt,
+ "/", LOOKUP_DOWN, &root);
+ if (err) {
+ /* revert to old namespace */
+ nsproxy->mnt_ns = old_mnt_ns;
+ put_mnt_ns(mnt_ns);
+ return err;
+ }
/* Update the pwd and root */
set_fs_pwd(fs, &root);
diff --git a/include/linux/namei.h b/include/linux/namei.h
index f29abda3..8b4794e 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -44,6 +44,7 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT, LAST_BIND};
#define LOOKUP_JUMPED 0x1000
#define LOOKUP_ROOT 0x2000
#define LOOKUP_EMPTY 0x4000
+#define LOOKUP_DOWN 0x8000
extern int path_pts(struct path *path);