Re: [PATCH, RFC] ath10k: Fix skb->len (properly) in ath10k_sdio_mbox_rx_packet

[Nicolas Boichat]

On Tue, Aug 27, 2019 at 11:34 AM Wen Gong <wgong@xxxxxxxxxxxxxxxx> wrote:
>
> > -----Original Message-----
> > From: ath10k <ath10k-bounces@xxxxxxxxxxxxxxxxxxx> On Behalf Of Nicolas
> > Boichat
> > Sent: Tuesday, August 27, 2019 8:33 AM
> > To: kvalo@xxxxxxxxxxxxxx
> > Cc: Alagu Sankar <alagusankar@xxxxxxxxxxxxxxx>; netdev@xxxxxxxxxxxxxxx;
> > briannorris@xxxxxxxxxxxx; linux-wireless@xxxxxxxxxxxxxxx; linux-
> > kernel@xxxxxxxxxxxxxxx; ath10k@xxxxxxxxxxxxxxxxxxx;
> > wgong@xxxxxxxxxxxxxx; niklas.cassel@xxxxxxxxxx; tientzu@xxxxxxxxxxxx;
> > David S . Miller <davem@xxxxxxxxxxxxx>
> > Subject: [EXT] [PATCH, RFC] ath10k: Fix skb->len (properly) in
> > ath10k_sdio_mbox_rx_packet
> >
> > (not a formal patch, take this as a bug report for now, I can clean
> > up depending on the feedback I get here)
> >
> > There's at least 3 issues here, and the patch fixes 2/3 only, I'm not sure
> > how/if 1 should be handled.
> >  1. ath10k_sdio_mbox_rx_alloc allocating skb of a incorrect size (too
> >     small)
> >  2. ath10k_sdio_mbox_rx_packet calling skb_put with that incorrect size.
> >  3. ath10k_sdio_mbox_rx_process_packet attempts to fixup the size, but
> >     does not use proper skb_put commands to do so, so we end up with
> >     a mismatch between skb->head + skb->tail and skb->data + skb->len.
> >
> > Let's start with 3, this is quite serious as this and causes corruptions
> > in the TCP stack, as the stack tries to coalesce packets, and relies on
> > skb->tail being correct (that is, skb_tail_pointer must point to the
> > first byte _after_ the data): one must never manipulate skb->len
> > directly.
> >
> > Instead, we need to use skb_put to allocate more space (which updates
> > skb->len and skb->tail). But it seems odd to do that in
> > ath10k_sdio_mbox_rx_process_packet, so I move the code to
> > ath10k_sdio_mbox_rx_packet (point 2 above).
> >
> > However, there is still something strange (point 1 above), why is
> > ath10k_sdio_mbox_rx_alloc allocating packets of the incorrect
> > (too small?) size? What happens if the packet is bigger than alloc_len?
> > Does this lead to corruption/lost data?
> >
> > Fixes: 8530b4e7b22bc3b ("ath10k: sdio: set skb len for all rx packets")
> > Signed-off-by: Nicolas Boichat <drinkcat@xxxxxxxxxxxx>
> >
> > ---
> >
> > One simple way to test this is this scriplet, that sends a lot of
> > small packets over SSH:
> > (for i in `seq 1 300`; do echo $i; sleep 0.1; done) | ssh $IP cat
> >
> > In my testing it rarely ever reach 300 without failure.
> >
> >  drivers/net/wireless/ath/ath10k/sdio.c | 18 ++++++++++++------
> >  1 file changed, 12 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/net/wireless/ath/ath10k/sdio.c
> > b/drivers/net/wireless/ath/ath10k/sdio.c
> > index 8ed4fbd8d6c3888..a9f5002863ee7bb 100644
> > --- a/drivers/net/wireless/ath/ath10k/sdio.c
> > +++ b/drivers/net/wireless/ath/ath10k/sdio.c
> > @@ -381,16 +381,14 @@ static int
> > ath10k_sdio_mbox_rx_process_packet(struct ath10k *ar,
> >       struct ath10k_htc_hdr *htc_hdr = (struct ath10k_htc_hdr *)skb->data;
> >       bool trailer_present = htc_hdr->flags &
> > ATH10K_HTC_FLAG_TRAILER_PRESENT;
> >       enum ath10k_htc_ep_id eid;
> > -     u16 payload_len;
> >       u8 *trailer;
> >       int ret;
> >
> > -     payload_len = le16_to_cpu(htc_hdr->len);
> > -     skb->len = payload_len + sizeof(struct ath10k_htc_hdr);
> > +     /* TODO: Remove this? */
> If the pkt->act_len has set again in ath10k_sdio_mbox_rx_packet, seems not needed.

Sure, will drop.

> > +     WARN_ON(skb->len != le16_to_cpu(htc_hdr->len) + sizeof(*htc_hdr));
> >
> >       if (trailer_present) {
> > -             trailer = skb->data + sizeof(*htc_hdr) +
> > -                       payload_len - htc_hdr->trailer_len;
> > +             trailer = skb->data + skb->len - htc_hdr->trailer_len;
> >
> >               eid = pipe_id_to_eid(htc_hdr->eid);
> >
> > @@ -637,8 +635,16 @@ static int ath10k_sdio_mbox_rx_packet(struct
> > ath10k *ar,
> >       ret = ath10k_sdio_readsb(ar, ar_sdio->mbox_info.htc_addr,
> >                                skb->data, pkt->alloc_len);
> >       pkt->status = ret;
> > -     if (!ret)
> > +     if (!ret) {
> > +             /* Update actual length. */
> > +             /* FIXME: This looks quite wrong, why is pkt->act_len not
> > +              * correct in the first place?
> > +              */
> Firmware will do bundle for rx packet, and the aligned length by block size(256) of each packet's len is same
> in a bundle.
>
> Eg.
> packet 1 len: 300, aligned length:512
> packet 2 len: 400, aligned length:512
> packet 3 len: 200, aligned length:256
> packet 4 len: 100, aligned length:256
> packet 5 len: 700, aligned length:768
> packet 6 len: 600, aligned length:768
>
> then packet 1,2 will in bundle 1, packet 3,4 in a bundle 2, packet 5,6 in a bundle 3.
>
> For bundle 1, packet 1,2 will both allocate with len 512, and act_len is 300 first,
> then packet 2's len will be overwrite to 400.
>
> For bundle 2, packet 3,4 will both allocate with len 256, and act_len is 200 first,
> then packet 4's len will be overwrite to 100.
>
> For bundle 3, packet 5,6 will both allocate with len 768, and act_len is 700 first,
> then packet 6's len will be overwrite to 600.

Ok thanks, I'll send a v2 with an improved description.

> > +             struct ath10k_htc_hdr *htc_hdr =
> > +                     (struct ath10k_htc_hdr *)skb->data;
> > +             pkt->act_len = le16_to_cpu(htc_hdr->len) + sizeof(*htc_hdr);
> >               skb_put(skb, pkt->act_len);
> > +     }
> >
> >       return ret;
> >  }
> > --
> > 2.23.0.187.g17f5b7556c-goog
> >
> >
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