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From c0ea161a6e7158281f64bc6d41126da43cb08f14 Mon Sep 17 00:00:00 2001
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From: "Eric W. Biederman" <ebiederm@xmission.com>
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Date: Sat, 15 Aug 2015 13:36:12 -0500
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Subject: [PATCH 1/2] dcache: Handle escaped paths in prepend_path
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commit cde93be45a8a90d8c264c776fab63487b5038a65 upstream.
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A rename can result in a dentry that by walking up d_parent
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will never reach it's mnt_root. For lack of a better term
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I call this an escaped path.
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prepend_path is called by four different functions __d_path,
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d_absolute_path, d_path, and getcwd.
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__d_path only wants to see paths are connected to the root it passes
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in. So __d_path needs prepend_path to return an error.
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d_absolute_path similarly wants to see paths that are connected to
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some root. Escaped paths are not connected to any mnt_root so
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d_absolute_path needs prepend_path to return an error greater
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than 1. So escaped paths will be treated like paths on lazily
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unmounted mounts.
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getcwd needs to prepend "(unreachable)" so getcwd also needs
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prepend_path to return an error.
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d_path is the interesting hold out. d_path just wants to print
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something, and does not care about the weird cases. Which raises
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the question what should be printed?
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Given that <escaped_path>/<anything> should result in -ENOENT I
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believe it is desirable for escaped paths to be printed as empty
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paths. As there are not really any meaninful path components when
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considered from the perspective of a mount tree.
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So tweak prepend_path to return an empty path with an new error
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code of 3 when it encounters an escaped path.
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Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
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Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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---
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fs/dcache.c | 7 +++++++
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1 file changed, 7 insertions(+)
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diff --git a/fs/dcache.c b/fs/dcache.c
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index 9b5fe503f6cb..e3b44ca75a1b 100644
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--- a/fs/dcache.c
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+++ b/fs/dcache.c
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@@ -2926,6 +2926,13 @@ restart:
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if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
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struct mount *parent = ACCESS_ONCE(mnt->mnt_parent);
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+ /* Escaped? */
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+ if (dentry != vfsmnt->mnt_root) {
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+ bptr = *buffer;
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+ blen = *buflen;
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+ error = 3;
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+ break;
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+ }
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/* Global root? */
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if (mnt != parent) {
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dentry = ACCESS_ONCE(mnt->mnt_mountpoint);
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--
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2.4.3
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