|
 |
c341a2b |
From 14588dfe2e411056df5ba85ef88ad51730a2fa0a Mon Sep 17 00:00:00 2001
|
|
|
c341a2b |
From: "Eric W. Biederman" <ebiederm@xmission.com>
|
|
|
c341a2b |
Date: Sat, 15 Aug 2015 20:27:13 -0500
|
|
|
c341a2b |
Subject: [PATCH 2/2] vfs: Test for and handle paths that are unreachable from
|
|
|
c341a2b |
their mnt_root
|
|
|
c341a2b |
|
|
|
c341a2b |
commit 397d425dc26da728396e66d392d5dcb8dac30c37 upstream.
|
|
|
c341a2b |
|
|
|
c341a2b |
In rare cases a directory can be renamed out from under a bind mount.
|
|
|
c341a2b |
In those cases without special handling it becomes possible to walk up
|
|
|
c341a2b |
the directory tree to the root dentry of the filesystem and down
|
|
|
c341a2b |
from the root dentry to every other file or directory on the filesystem.
|
|
|
c341a2b |
|
|
|
c341a2b |
Like division by zero .. from an unconnected path can not be given
|
|
|
c341a2b |
a useful semantic as there is no predicting at which path component
|
|
|
c341a2b |
the code will realize it is unconnected. We certainly can not match
|
|
|
c341a2b |
the current behavior as the current behavior is a security hole.
|
|
|
c341a2b |
|
|
|
c341a2b |
Therefore when encounting .. when following an unconnected path
|
|
|
c341a2b |
return -ENOENT.
|
|
|
c341a2b |
|
|
|
c341a2b |
- Add a function path_connected to verify path->dentry is reachable
|
|
|
c341a2b |
from path->mnt.mnt_root. AKA to validate that rename did not do
|
|
|
c341a2b |
something nasty to the bind mount.
|
|
|
c341a2b |
|
|
|
c341a2b |
To avoid races path_connected must be called after following a path
|
|
|
c341a2b |
component to it's next path component.
|
|
|
c341a2b |
|
|
|
c341a2b |
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
|
|
|
c341a2b |
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
|
|
|
c341a2b |
---
|
|
|
c341a2b |
fs/namei.c | 27 +++++++++++++++++++++++++--
|
|
|
c341a2b |
1 file changed, 25 insertions(+), 2 deletions(-)
|
|
|
c341a2b |
|
|
|
c341a2b |
diff --git a/fs/namei.c b/fs/namei.c
|
|
|
c341a2b |
index 1c2105ed20c5..29b927938b8c 100644
|
|
|
c341a2b |
--- a/fs/namei.c
|
|
|
c341a2b |
+++ b/fs/namei.c
|
|
|
c341a2b |
@@ -560,6 +560,24 @@ static int __nd_alloc_stack(struct nameidata *nd)
|
|
|
c341a2b |
return 0;
|
|
|
c341a2b |
}
|
|
|
c341a2b |
|
|
|
c341a2b |
+/**
|
|
|
c341a2b |
+ * path_connected - Verify that a path->dentry is below path->mnt.mnt_root
|
|
|
c341a2b |
+ * @path: nameidate to verify
|
|
|
c341a2b |
+ *
|
|
|
c341a2b |
+ * Rename can sometimes move a file or directory outside of a bind
|
|
|
c341a2b |
+ * mount, path_connected allows those cases to be detected.
|
|
|
c341a2b |
+ */
|
|
|
c341a2b |
+static bool path_connected(const struct path *path)
|
|
|
c341a2b |
+{
|
|
|
c341a2b |
+ struct vfsmount *mnt = path->mnt;
|
|
|
c341a2b |
+
|
|
|
c341a2b |
+ /* Only bind mounts can have disconnected paths */
|
|
|
c341a2b |
+ if (mnt->mnt_root == mnt->mnt_sb->s_root)
|
|
|
c341a2b |
+ return true;
|
|
|
c341a2b |
+
|
|
|
c341a2b |
+ return is_subdir(path->dentry, mnt->mnt_root);
|
|
|
c341a2b |
+}
|
|
|
c341a2b |
+
|
|
|
c341a2b |
static inline int nd_alloc_stack(struct nameidata *nd)
|
|
|
c341a2b |
{
|
|
|
c341a2b |
if (likely(nd->depth != EMBEDDED_LEVELS))
|
|
|
c341a2b |
@@ -1296,6 +1314,8 @@ static int follow_dotdot_rcu(struct nameidata *nd)
|
|
|
c341a2b |
return -ECHILD;
|
|
|
c341a2b |
nd->path.dentry = parent;
|
|
|
c341a2b |
nd->seq = seq;
|
|
|
c341a2b |
+ if (unlikely(!path_connected(&nd->path)))
|
|
|
c341a2b |
+ return -ENOENT;
|
|
|
c341a2b |
break;
|
|
|
c341a2b |
} else {
|
|
|
c341a2b |
struct mount *mnt = real_mount(nd->path.mnt);
|
|
|
c341a2b |
@@ -1396,7 +1416,7 @@ static void follow_mount(struct path *path)
|
|
|
c341a2b |
}
|
|
|
c341a2b |
}
|
|
|
c341a2b |
|
|
|
c341a2b |
-static void follow_dotdot(struct nameidata *nd)
|
|
|
c341a2b |
+static int follow_dotdot(struct nameidata *nd)
|
|
|
c341a2b |
{
|
|
|
c341a2b |
if (!nd->root.mnt)
|
|
|
c341a2b |
set_root(nd);
|
|
|
c341a2b |
@@ -1412,6 +1432,8 @@ static void follow_dotdot(struct nameidata *nd)
|
|
|
c341a2b |
/* rare case of legitimate dget_parent()... */
|
|
|
c341a2b |
nd->path.dentry = dget_parent(nd->path.dentry);
|
|
|
c341a2b |
dput(old);
|
|
|
c341a2b |
+ if (unlikely(!path_connected(&nd->path)))
|
|
|
c341a2b |
+ return -ENOENT;
|
|
|
c341a2b |
break;
|
|
|
c341a2b |
}
|
|
|
c341a2b |
if (!follow_up(&nd->path))
|
|
|
c341a2b |
@@ -1419,6 +1441,7 @@ static void follow_dotdot(struct nameidata *nd)
|
|
|
c341a2b |
}
|
|
|
c341a2b |
follow_mount(&nd->path);
|
|
|
c341a2b |
nd->inode = nd->path.dentry->d_inode;
|
|
|
c341a2b |
+ return 0;
|
|
|
c341a2b |
}
|
|
|
c341a2b |
|
|
|
c341a2b |
/*
|
|
|
c341a2b |
@@ -1634,7 +1657,7 @@ static inline int handle_dots(struct nameidata *nd, int type)
|
|
|
c341a2b |
if (nd->flags & LOOKUP_RCU) {
|
|
|
c341a2b |
return follow_dotdot_rcu(nd);
|
|
|
c341a2b |
} else
|
|
|
c341a2b |
- follow_dotdot(nd);
|
|
|
c341a2b |
+ return follow_dotdot(nd);
|
|
|
c341a2b |
}
|
|
|
c341a2b |
return 0;
|
|
|
c341a2b |
}
|
|
|
c341a2b |
--
|
|
|
c341a2b |
2.4.3
|
|
|
c341a2b |
|