Patch "nfsd4: fix null dereference on replay" has been added to the 4.4-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    nfsd4: fix null dereference on replay

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     nfsd4-fix-null-dereference-on-replay.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 9a307403d374b993061f5992a6e260c944920d0b Mon Sep 17 00:00:00 2001
From: "J. Bruce Fields" <bfields@redhat.com>
Date: Tue, 23 May 2017 12:24:40 -0400
Subject: nfsd4: fix null dereference on replay

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

commit 9a307403d374b993061f5992a6e260c944920d0b upstream.

if we receive a compound such that:

	- the sessionid, slot, and sequence number in the SEQUENCE op
	  match a cached succesful reply with N ops, and
	- the Nth operation of the compound is a PUTFH, PUTPUBFH,
	  PUTROOTFH, or RESTOREFH,

then nfsd4_sequence will return 0 and set cstate->status to
nfserr_replay_cache.  The current filehandle will not be set.  This will
cause us to call check_nfsd_access with first argument NULL.

To nfsd4_compound it looks like we just succesfully executed an
operation that set a filehandle, but the current filehandle is not set.

Fix this by moving the nfserr_replay_cache earlier.  There was never any
reason to have it after the encode_op label, since the only case where
he hit that is when opdesc->op_func sets it.

Note that there are two ways we could hit this case:

	- a client is resending a previously sent compound that ended
	  with one of the four PUTFH-like operations, or
	- a client is sending a *new* compound that (incorrectly) shares
	  sessionid, slot, and sequence number with a previously sent
	  compound, and the length of the previously sent compound
	  happens to match the position of a PUTFH-like operation in the
	  new compound.

The second is obviously incorrect client behavior.  The first is also
very strange--the only purpose of a PUTFH-like operation is to set the
current filehandle to be used by the following operation, so there's no
point in having it as the last in a compound.

So it's likely this requires a buggy or malicious client to reproduce.

Reported-by: Scott Mayhew <smayhew@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/nfsd/nfs4proc.c |   13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -1690,6 +1690,12 @@ nfsd4_proc_compound(struct svc_rqst *rqs
 			opdesc->op_get_currentstateid(cstate, &op->u);
 		op->status = opdesc->op_func(rqstp, cstate, &op->u);
 
+		/* Only from SEQUENCE */
+		if (cstate->status == nfserr_replay_cache) {
+			dprintk("%s NFS4.1 replay from cache\n", __func__);
+			status = op->status;
+			goto out;
+		}
 		if (!op->status) {
 			if (opdesc->op_set_currentstateid)
 				opdesc->op_set_currentstateid(cstate, &op->u);
@@ -1700,14 +1706,7 @@ nfsd4_proc_compound(struct svc_rqst *rqs
 			if (need_wrongsec_check(rqstp))
 				op->status = check_nfsd_access(current_fh->fh_export, rqstp);
 		}
-
 encode_op:
-		/* Only from SEQUENCE */
-		if (cstate->status == nfserr_replay_cache) {
-			dprintk("%s NFS4.1 replay from cache\n", __func__);
-			status = op->status;
-			goto out;
-		}
 		if (op->status == nfserr_replay_me) {
 			op->replay = &cstate->replay_owner->so_replay;
 			nfsd4_encode_replay(&resp->xdr, op);


Patches currently in stable-queue which might be from bfields@redhat.com are

queue-4.4/nfsd4-fix-null-dereference-on-replay.patch
queue-4.4/nfsd-fix-up-the-supattr_exclcreat-attributes.patch