From c0ea161a6e7158281f64bc6d41126da43cb08f14 Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Sat, 15 Aug 2015 13:36:12 -0500 Subject: [PATCH 1/2] dcache: Handle escaped paths in prepend_path 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 / 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" Signed-off-by: Al Viro --- fs/dcache.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/fs/dcache.c b/fs/dcache.c index 9b5fe503f6cb..e3b44ca75a1b 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -2926,6 +2926,13 @@ 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); -- 2.4.3