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 <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>
[bwh: For 2.6.32, implement the "(unreachable)" string in __d_path()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Willy Tarreau <w@1wt.eu>

diff --git a/fs/dcache.c b/fs/dcache.c
index 44c0aeafcbc955205f94620bd51dcd7612f99eca..07c4472ca62c6394bc2858714f1531a443c17403 100644 (file)
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1910,7 +1910,7 @@ char *__d_path(const struct path *path, struct path *root,
        struct dentry *dentry = path->dentry;
        struct vfsmount *vfsmnt = path->mnt;
        char *end = buffer + buflen;
-       char *retval;
+       char *retval, *tail;
 
        spin_lock(&vfsmount_lock);
        prepend(&end, &buflen, "\0", 1);
@@ -1923,6 +1923,7 @@ char *__d_path(const struct path *path, struct path *root,
        /* Get '/' right */
        retval = end-1;
        *retval = '/';
+       tail = end;
 
        for (;;) {
                struct dentry * parent;
@@ -1930,6 +1931,14 @@ char *__d_path(const struct path *path, struct path *root,
                if (dentry == root->dentry && vfsmnt == root->mnt)
                        break;
                if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
+                       /* Escaped? */
+                       if (dentry != vfsmnt->mnt_root) {
+                               buflen += (tail - end);
+                               end = tail;
+                               prepend(&end, &buflen, "(unreachable)/", 14);
+                               retval = end;
+                               goto out;
+                       }
                        /* Global root? */
                        if (vfsmnt->mnt_parent == vfsmnt) {
                                goto global_root;