linux-kernel - [PATCH 5.5 013/399] nfsd4: avoid NULL deference on strange COPY compounds

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Message-Id: <20200221072403.604900959@linuxfoundation.org>
Date:   Fri, 21 Feb 2020 08:35:38 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Dan Carpenter <dan.carpenter@...cle.com>,
        "J. Bruce Fields" <bfields@...hat.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.5 013/399] nfsd4: avoid NULL deference on strange COPY compounds

From: J. Bruce Fields <bfields@...hat.com>

[ Upstream commit d781e3df710745fbbaee4eb07fd5b64331a1b175 ]

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)
	GETATTR
	SAVEFH
	COPY

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@...cle.com>
Fixes: 4e48f1cccab3 "NFSD: allow inter server COPY to have... "
Signed-off-by: J. Bruce Fields <bfields@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/nfsd/nfs4proc.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index 4798667af647c..4d1d0bf8e385f 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -2025,7 +2025,8 @@ nfsd4_proc_compound(struct svc_rqst *rqstp)
 			if (op->opdesc->op_flags & OP_CLEAR_STATEID)
 				clear_current_stateid(cstate);

-			if (need_wrongsec_check(rqstp))
+			if (current_fh->fh_export &&
+					need_wrongsec_check(rqstp))
 				op->status = check_nfsd_access(current_fh->fh_export, rqstp);
 		}
 encode_op:
-- 
2.20.1