--- /dev/null
+From cde93be45a8a90d8c264c776fab63487b5038a65 Mon Sep 17 00:00:00 2001
+From: "Eric W. Biederman" <ebiederm@xmission.com>
+Date: Sat, 15 Aug 2015 13:36:12 -0500
+Subject: dcache: Handle escaped paths in prepend_path
+
+From: "Eric W. Biederman" <ebiederm@xmission.com>
+
+commit cde93be45a8a90d8c264c776fab63487b5038a65 upstream.
+
+A rename can result in a dentry that by walking up d_parent
+will never reach it's mnt_root. For lack of a better term
+I call this an escaped path.
+
+prepend_path is called by four different functions __d_path,
+d_absolute_path, d_path, and getcwd.
+
+__d_path only wants to see paths are connected to the root it passes
+in. So __d_path needs prepend_path to return an error.
+
+d_absolute_path similarly wants to see paths that are connected to
+some root. Escaped paths are not connected to any mnt_root so
+d_absolute_path needs prepend_path to return an error greater
+than 1. So escaped paths will be treated like paths on lazily
+unmounted mounts.
+
+getcwd needs to prepend "(unreachable)" so getcwd also needs
+prepend_path to return an error.
+
+d_path is the interesting hold out. d_path just wants to print
+something, and does not care about the weird cases. Which raises
+the question what should be printed?
+
+Given that <escaped_path>/<anything> should result in -ENOENT I
+believe it is desirable for escaped paths to be printed as empty
+paths. As there are not really any meaninful path components when
+considered from the perspective of a mount tree.
+
+So tweak prepend_path to return an empty path with an new error
+code of 3 when it encounters an escaped path.
+
+Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
+Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+
+---
+ fs/dcache.c | 7 +++++++
+ 1 file changed, 7 insertions(+)
+
+--- a/fs/dcache.c
++++ b/fs/dcache.c
+@@ -2787,6 +2787,13 @@ restart:
+
+ if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
+ struct mount *parent = ACCESS_ONCE(mnt->mnt_parent);
++ /* Escaped? */
++ if (dentry != vfsmnt->mnt_root) {
++ bptr = *buffer;
++ blen = *buflen;
++ error = 3;
++ break;
++ }
+ /* Global root? */
+ if (mnt != parent) {
+ dentry = ACCESS_ONCE(mnt->mnt_mountpoint);
--- /dev/null
+From 397d425dc26da728396e66d392d5dcb8dac30c37 Mon Sep 17 00:00:00 2001
+From: "Eric W. Biederman" <ebiederm@xmission.com>
+Date: Sat, 15 Aug 2015 20:27:13 -0500
+Subject: vfs: Test for and handle paths that are unreachable from their mnt_root
+
+From: "Eric W. Biederman" <ebiederm@xmission.com>
+
+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>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+
+
+---
+ fs/namei.c | 31 ++++++++++++++++++++++++++++---
+ 1 file changed, 28 insertions(+), 3 deletions(-)
+
+--- a/fs/namei.c
++++ b/fs/namei.c
+@@ -484,6 +484,24 @@ 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
+@@ -1149,6 +1167,8 @@ static int follow_dotdot_rcu(struct name
+ goto failed;
+ nd->path.dentry = parent;
+ nd->seq = seq;
++ if (unlikely(!path_connected(&nd->path)))
++ goto failed;
+ break;
+ }
+ if (!follow_up_rcu(&nd->path))
+@@ -1242,7 +1262,7 @@ static void follow_mount(struct path *pa
+ }
+ }
+
+-static void follow_dotdot(struct nameidata *nd)
++static int follow_dotdot(struct nameidata *nd)
+ {
+ if (!nd->root.mnt)
+ set_root(nd);
+@@ -1258,6 +1278,10 @@ static void follow_dotdot(struct nameida
+ /* 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))
+@@ -1265,6 +1289,7 @@ static void follow_dotdot(struct nameida
+ }
+ follow_mount(&nd->path);
+ nd->inode = nd->path.dentry->d_inode;
++ return 0;
+ }
+
+ /*
+@@ -1488,7 +1513,7 @@ static inline int handle_dots(struct nam
+ if (follow_dotdot_rcu(nd))
+ return -ECHILD;
+ } else
+- follow_dotdot(nd);
++ return follow_dotdot(nd);
+ }
+ return 0;
+ }
+@@ -2214,7 +2239,7 @@ mountpoint_last(struct nameidata *nd, st
+ 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;
+ }
projects / thirdparty / kernel / stable-queue.git / commitdiff
