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Date:   Tue, 10 Jul 2018 01:54:03 +0200
From:   Dominique Martinet <asmadeus@codewreck.org>
To:     Tomas Bortoli <tomasbortoli@gmail.com>
Cc:     ericvh@gmail.com, rminnich@sandia.gov, lucho@ionkov.net,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        syzkaller@googlegroups.com, v9fs-developer@lists.sourceforge.net,
        davem@davemloft.net, Al Viro <viro@ZenIV.linux.org.uk>
Subject: Re: [V9fs-developer]  [PATCH] p9_check_errors() validate PDU length
Message-ID: <20180709235403.GB19917@nautica>
References: <20180709224323.20597-1-tomasbortoli@gmail.com>
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(extra Cc: Al Viro, as it's kind of the continuation of the other
thread)

Tomas Bortoli wrote on Tue, Jul 10, 2018:
> p9_check_errors() does not validate the size of the PDU read
> in p9_parse_header(). Any size can be passed, provoking out-of-bound reads.

cf. what I just said in other patch, I think this check needs to be
moved up to p9_parse_header as p9_check_zc_error has the same problem.

Also, they really need to check against the actual read size, not just
capacity.
For virtio/rdma, something like this ought to fix pdu->size, then
p9_parse_header can just never overwrite it (untested but it's useless
on its own, I'll test the full patch with the parse header change)

diff --git a/net/9p/trans_rdma.c b/net/9p/trans_rdma.c
index 3d414acb7015..2649b2ebf961 100644
--- a/net/9p/trans_rdma.c
+++ b/net/9p/trans_rdma.c
@@ -320,6 +320,7 @@ recv_done(struct ib_cq *cq, struct ib_wc *wc)
 	if (wc->status != IB_WC_SUCCESS)
 		goto err_out;
 
+	c->rc->size = wc->byte_len;
 	err = p9_parse_header(c->rc, NULL, NULL, &tag, 1);
 	if (err)
 		goto err_out;
diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
index 05006cbb3361..fc6dc9ca86a4 100644
--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -159,8 +159,10 @@ static void req_done(struct virtqueue *vq)
 		spin_unlock_irqrestore(&chan->lock, flags);
 		/* Wakeup if anyone waiting for VirtIO ring space. */
 		wake_up(chan->vc_wq);
-		if (len)
+		if (len) {
+			req->rc->size = len;
 			p9_client_cb(chan->client, req, REQ_STATUS_RCVD);
+		}
 	}
 }
-- 
Dominique Martinet | Asmadeus