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authorEric W. Biederman <ebiederm@xmission.com>2015-08-15 20:27:13 -0500
committerZefan Li <lizefan@huawei.com>2015-10-22 09:20:08 +0800
commit4a69710b414cd12081da97ec35971c9b22833992 (patch)
treee8e46ffe54817bc3c50873ed0b18f40af4fd09eb
parent652b4f2f20702cbb6cb7846a39af99d182c59764 (diff)
downloadlwn-4a69710b414cd12081da97ec35971c9b22833992.tar.gz
lwn-4a69710b414cd12081da97ec35971c9b22833992.zip
vfs: Test for and handle paths that are unreachable from their mnt_root
commit 397d425dc26da728396e66d392d5dcb8dac30c37 upstream. In rare cases a directory can be renamed out from under a bind mount. In those cases without special handling it becomes possible to walk up the directory tree to the root dentry of the filesystem and down from the root dentry to every other file or directory on the filesystem. Like division by zero .. from an unconnected path can not be given a useful semantic as there is no predicting at which path component the code will realize it is unconnected. We certainly can not match the current behavior as the current behavior is a security hole. Therefore when encounting .. when following an unconnected path return -ENOENT. - Add a function path_connected to verify path->dentry is reachable from path->mnt.mnt_root. AKA to validate that rename did not do something nasty to the bind mount. To avoid races path_connected must be called after following a path component to it's next path component. Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
-rw-r--r--fs/namei.c29
1 files changed, 27 insertions, 2 deletions
diff --git a/fs/namei.c b/fs/namei.c
index 9c4b9b811d7b..4fc034ffd209 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -397,6 +397,24 @@ void path_put(struct path *path)
}
EXPORT_SYMBOL(path_put);
+/**
+ * path_connected - Verify that a path->dentry is below path->mnt.mnt_root
+ * @path: nameidate to verify
+ *
+ * Rename can sometimes move a file or directory outside of a bind
+ * mount, path_connected allows those cases to be detected.
+ */
+static bool path_connected(const struct path *path)
+{
+ struct vfsmount *mnt = path->mnt;
+
+ /* Only bind mounts can have disconnected paths */
+ if (mnt->mnt_root == mnt->mnt_sb->s_root)
+ return true;
+
+ return is_subdir(path->dentry, mnt->mnt_root);
+}
+
/*
* Path walking has 2 modes, rcu-walk and ref-walk (see
* Documentation/filesystems/path-lookup.txt). In situations when we can't
@@ -945,6 +963,8 @@ static int follow_dotdot_rcu(struct nameidata *nd)
goto failed;
nd->path.dentry = parent;
nd->seq = seq;
+ if (unlikely(!path_connected(&nd->path)))
+ goto failed;
break;
}
if (!follow_up_rcu(&nd->path))
@@ -1029,7 +1049,7 @@ static void follow_mount(struct path *path)
}
}
-static void follow_dotdot(struct nameidata *nd)
+static int follow_dotdot(struct nameidata *nd)
{
if (!nd->root.mnt)
set_root(nd);
@@ -1045,6 +1065,10 @@ static void follow_dotdot(struct nameidata *nd)
/* rare case of legitimate dget_parent()... */
nd->path.dentry = dget_parent(nd->path.dentry);
dput(old);
+ if (unlikely(!path_connected(&nd->path))) {
+ path_put(&nd->path);
+ return -ENOENT;
+ }
break;
}
if (!follow_up(&nd->path))
@@ -1052,6 +1076,7 @@ static void follow_dotdot(struct nameidata *nd)
}
follow_mount(&nd->path);
nd->inode = nd->path.dentry->d_inode;
+ return 0;
}
/*
@@ -1252,7 +1277,7 @@ static inline int handle_dots(struct nameidata *nd, int type)
if (follow_dotdot_rcu(nd))
return -ECHILD;
} else
- follow_dotdot(nd);
+ return follow_dotdot(nd);
}
return 0;
}