Re: [PATCH] 9p: validate PDU length

Dominique Martinet
2018-07-24T03:57:36Z

Tomas Bortoli wrote on Mon, Jul 23, 2018:
> This commit adds length check for the PDU size.
> The size contained in the header has to match the actual size,
> except for TCP (trans_fd.c) where actual length is not known ahead
> and the header's length will be checked only against the validity
> range.
>
> Signed-off-by: Tomas Bortoli <tomasbortoli@gmail.com>
> Reported-by: syzbot+65c6b72f284a39d416b4@syzkaller.appspotmail.com

Ok, I've run some more in-depth testing this time and all appear in
order.
Like I said last time, I cannot test the xen transport - if someone can
point me to how to set it up or run some tests semi-regularily it'd be
great.

Meanwhile, code looks good and appears to work, so I'll take this
patch unless someone yells

> ---
> net/9p/client.c | 25 ++++++++++++++++---------
> net/9p/trans_fd.c | 5 ++++-
> net/9p/trans_rdma.c | 1 +
> net/9p/trans_virtio.c | 4 +++-
> 4 files changed, 24 insertions(+), 11 deletions(-)
>
> diff --git a/net/9p/client.c b/net/9p/client.c
> index 18c5271910dc..92240ccf476b 100644
> --- a/net/9p/client.c
> +++ b/net/9p/client.c
> @@ -477,20 +477,11 @@ p9_parse_header(struct p9_fcall *pdu, int32_t *size, int8_t *type, int16_t *tag,
> int err;
>
> pdu->offset = 0;
> - if (pdu->size == 0)
> - pdu->size = 7;
>
> err = p9pdu_readf(pdu, 0, "dbw", &r_size, &r_type, &r_tag);
> if (err)
> goto rewind_and_exit;
>
> - pdu->size = r_size;
> - pdu->id = r_type;
> - pdu->tag = r_tag;
> -
> - p9_debug(P9_DEBUG_9P, "<<< size=%d type: %d tag: %d\n",
> - pdu->size, pdu->id, pdu->tag);
> -
> if (type)
> *type = r_type;
> if (tag)
> @@ -498,6 +489,16 @@ p9_parse_header(struct p9_fcall *pdu, int32_t *size, int8_t *type, int16_t *tag,
> if (size)
> *size = r_size;
>
> + if (pdu->size != r_size || r_size < 7) {
> + err = -EINVAL;
> + goto rewind_and_exit;
> + }
> +
> + pdu->id = r_type;
> + pdu->tag = r_tag;
> +
> + p9_debug(P9_DEBUG_9P, "<<< size=%d type: %d tag: %d\n",
> + pdu->size, pdu->id, pdu->tag);
>
> rewind_and_exit:
> if (rewind)
> @@ -524,6 +525,12 @@ static int p9_check_errors(struct p9_client *c, struct p9_req_t *req)
> int ecode;
>
> err = p9_parse_header(req->rc, NULL, &type, NULL, 0);
> + if (req->rc->size >= c->msize) {
> + p9_debug(P9_DEBUG_ERROR,
> + "requested packet size too big: %d\n",
> + req->rc->size);
> + return -EIO;

Indentation here looks wrong, I took the liberty of deindenting that
return in my tree.

> + }
> /*
> * dump the response from server
> * This should be after check errors which poplulate pdu_fcall.
> diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c
> index 588bf88c3305..65533c437b7f 100644
> --- a/net/9p/trans_fd.c
> +++ b/net/9p/trans_fd.c
> @@ -324,7 +324,9 @@ static void p9_read_work(struct work_struct *work)
> if ((!m->req) && (m->rc.offset == m->rc.capacity)) {
> p9_debug(P9_DEBUG_TRANS, "got new header\n");
>
> - err = p9_parse_header(&m->rc, NULL, NULL, NULL, 0);
> + /* Header size */
> + m->rc.size = 7;
> + err = p9_parse_header(&m->rc, &m->rc.size, NULL, NULL, 0);
> if (err) {
> p9_debug(P9_DEBUG_ERROR,
> "error parsing header: %d\n", err);
> @@ -369,6 +371,7 @@ static void p9_read_work(struct work_struct *work)
> */
> if ((m->req) && (m->rc.offset == m->rc.capacity)) {
> p9_debug(P9_DEBUG_TRANS, "got new packet\n");
> + m->req->rc->size = m->rc.offset;
> spin_lock(&m->client->lock);
> if (m->req->status != REQ_STATUS_ERROR)
> status = REQ_STATUS_RCVD;
> 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