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dcache: Handle escaped paths in prepend_path

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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>
This commit is contained in:
Eric W. Biederman 2015-08-15 13:36:12 -05:00 committed by Greg Kroah-Hartman
parent ef5844a015
commit 91397d5676
1 changed files with 10 additions and 0 deletions
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10
fs/dcache.c
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@ -2534,6 +2534,8 @@ static int prepend_path(const struct path *path,
struct dentry *dentry = path->dentry;
struct vfsmount *vfsmnt = path->mnt;
struct mount *mnt = real_mount(vfsmnt);
char *orig_buffer = *buffer;
int orig_len = *buflen;
bool slash = false;
int error = 0;
@ -2541,6 +2543,14 @@ static int prepend_path(const struct path *path,
struct dentry * parent;
if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
/* Escaped? */
if (dentry != vfsmnt->mnt_root) {
*buffer = orig_buffer;
*buflen = orig_len;
slash = false;
error = 3;
goto global_root;
}
/* Global root? */
if (!mnt_has_parent(mnt))
goto global_root;