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authorEric W. Biederman <ebiederm@xmission.com>2015-08-15 20:27:13 -0500
committerSasha Levin <sasha.levin@oracle.com>2015-10-27 22:14:58 -0400
commit7f61fd99a60195578215f46ed870b5c118cfbfc0 (patch)
tree5b80d60ba8c1107cdfa5bbd63072b53027dc55b1
parent3e6fba2fc343ef5d80f751b699a4688a2f57f861 (diff)
downloadlinux-linaro-stable-7f61fd99a60195578215f46ed870b5c118cfbfc0.tar.gz
vfs: Test for and handle paths that are unreachable from their mnt_root
[ Upstream commit 397d425dc26da728396e66d392d5dcb8dac30c37 ] 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> Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
-rw-r--r--fs/namei.c31
1 files changed, 28 insertions, 3 deletions
diff --git a/fs/namei.c b/fs/namei.c
index d20f061cddd3..be3d538d56b3 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -487,6 +487,24 @@ void path_put(const 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
@@ -1164,6 +1182,8 @@ 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))
@@ -1260,7 +1280,7 @@ 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);
@@ -1276,6 +1296,10 @@ 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))
@@ -1283,6 +1307,7 @@ static void follow_dotdot(struct nameidata *nd)
}
follow_mount(&nd->path);
nd->inode = nd->path.dentry->d_inode;
+ return 0;
}
/*
@@ -1503,7 +1528,7 @@ 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;
}
@@ -2239,7 +2264,7 @@ mountpoint_last(struct nameidata *nd, struct path *path)
if (unlikely(nd->last_type != LAST_NORM)) {
error = handle_dots(nd, nd->last_type);
if (error)
- goto out;
+ return error;
dentry = dget(nd->path.dentry);
goto done;
}