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

From: Greg Kroah-Hartman
Date: Fri Feb 21 2020 - 03:18:25 EST

From: J. Bruce Fields <bfields@xxxxxxxxxx>

[ 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)

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... "
Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
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 f35aa9f88b5ec..895123518fd42 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -1789,7 +1789,8 @@ nfsd4_proc_compound(struct svc_rqst *rqstp)
if (op->opdesc->op_flags & OP_CLEAR_STATEID)

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