Re: [PATCH 4.19 011/191] nfsd4: avoid NULL deference on strange COPY compounds

From: Sasha Levin
Date: Sat Feb 22 2020 - 14:02:10 EST

On Fri, Feb 21, 2020 at 11:51:04AM +0100, Pavel Machek wrote:

With cross-server COPY we've introduced the possibility that the current
or saved filehandle might not have fh_dentry/fh_export filled in, but we
missed a place that assumed it was. I think this could be triggered by
a compound like:

PUTFH(foreign filehandle)

First, check_if_stalefh_allowed sets no_verify on the first (PUTFH) op.
Then op_func = nfsd4_putfh runs and leaves current_fh->fh_export NULL.
need_wrongsec_check returns true, since this PUTFH has OP_IS_PUTFH_LIKE
set and GETATTR does not have OP_HANDLES_WRONGSEC set.

We should probably also consider tightening the checks in
check_if_stalefh_allowed and double-checking that we don't assume the
filehandle is verified elsewhere in the compound. But I think this
fixes the immediate issue.

Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Fixes: 4e48f1cccab3 "NFSD: allow inter server COPY to have... "

AFAICT 4e48f1cccab3 "NFSD: allow inter server COPY to have... " is not
part of 4.19 series, so this should not be needed in 4.19.

Not only 4e48f1cccab3 isn't in 4.19, it isn't in any tree! :)

Looks like an error in the patch, I'll drop this commit from everywhere.