linux-kernel - [096/244] net/9p: Fix kernel crash with msize 512K

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Date:	Wed, 28 Sep 2011 15:01:00 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Eric Van Hensbergen <ericvh@...il.com>
Subject: [096/244] net/9p: Fix kernel crash with msize 512K

3.0-stable review patch.  If anyone has any objections, please let us know.

------------------

From: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>

commit b49d8b5d7007a673796f3f99688b46931293873e upstream.

With msize equal to 512K (PAGE_SIZE * VIRTQUEUE_NUM), we hit multiple
crashes. This patch fix those.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
Signed-off-by: Eric Van Hensbergen <ericvh@...il.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 net/9p/trans_virtio.c |   17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -263,7 +263,6 @@ p9_virtio_request(struct p9_client *clie
 {
 	int in, out, inp, outp;
 	struct virtio_chan *chan = client->trans;
-	char *rdata = (char *)req->rc+sizeof(struct p9_fcall);
 	unsigned long flags;
 	size_t pdata_off = 0;
 	struct trans_rpage_info *rpinfo = NULL;
@@ -346,7 +345,8 @@ req_retry_pinned:
 		 * Arrange in such a way that server places header in the
 		 * alloced memory and payload onto the user buffer.
 		 */
-		inp = pack_sg_list(chan->sg, out, VIRTQUEUE_NUM, rdata, 11);
+		inp = pack_sg_list(chan->sg, out,
+				   VIRTQUEUE_NUM, req->rc->sdata, 11);
 		/*
 		 * Running executables in the filesystem may result in
 		 * a read request with kernel buffer as opposed to user buffer.
@@ -366,8 +366,8 @@ req_retry_pinned:
 		}
 		in += inp;
 	} else {
-		in = pack_sg_list(chan->sg, out, VIRTQUEUE_NUM, rdata,
-				req->rc->capacity);
+		in = pack_sg_list(chan->sg, out, VIRTQUEUE_NUM,
+				  req->rc->sdata, req->rc->capacity);
 	}
 
 	err = virtqueue_add_buf(chan->vq, chan->sg, out, in, req->tc);
@@ -592,7 +592,14 @@ static struct p9_trans_module p9_virtio_
 	.close = p9_virtio_close,
 	.request = p9_virtio_request,
 	.cancel = p9_virtio_cancel,
-	.maxsize = PAGE_SIZE*VIRTQUEUE_NUM,
+
+	/*
+	 * We leave one entry for input and one entry for response
+	 * headers. We also skip one more entry to accomodate, address
+	 * that are not at page boundary, that can result in an extra
+	 * page in zero copy.
+	 */
+	.maxsize = PAGE_SIZE * (VIRTQUEUE_NUM - 3),
 	.pref = P9_TRANS_PREF_PAYLOAD_SEP,
 	.def = 0,
 	.owner = THIS_MODULE,


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