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nfsd4: readdirplus shouldn't return parent of export 

commit 51b2ee7d00 upstream.

If you export a subdirectory of a filesystem, a READDIRPLUS on the root
of that export will return the filehandle of the parent with the ".."
entry.

The filehandle is optional, so let's just not return the filehandle for
".." if we're at the root of an export.

Note that once the client learns one filehandle outside of the export,
they can trivially access the rest of the export using further lookups.

However, it is also not very difficult to guess filehandles outside of
the export.  So exporting a subdirectory of a filesystem should
considered equivalent to providing access to the entire filesystem.  To
avoid confusion, we recommend only exporting entire filesystems.

Reported-by: Youjipeng <wangzhibei1999@gmail.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
5.4-rM2-2.2.x-imx-squashed
J. Bruce Fields 2021-01-11 16:01:29 -05:00 committed by Greg Kroah-Hartman
parent 9b72d5ba50
commit 4aef760c28
1 changed files with 6 additions and 1 deletions
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7
fs/nfsd/nfs3xdr.c
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@ -857,9 +857,14 @@ compose_entry_fh(struct nfsd3_readdirres *cd, struct svc_fh *fhp,
if (isdotent(name, namlen)) {
if (namlen == 2) {
dchild = dget_parent(dparent);
/* filesystem root - cannot return filehandle for ".." */
/*
* Don't return filehandle for ".." if we're at
* the filesystem or export root:
*/
if (dchild == dparent)
goto out;
if (dparent == exp->ex_path.dentry)
goto out;
} else
dchild = dget(dparent);
} else