[PATCH v2] ath10k: Adjust skb length in ath10k_sdio_mbox_rx_packet

[Nicolas Boichat <drinkcat@chromium.org>]

When the FW bundles multiple packets, pkt->act_len may be incorrect
as it refers to the first packet only (however, the FW will only
bundle packets that fit into the same pkt->alloc_len).

Before this patch, the skb length would be set (incorrectly) to
pkt->act_len in ath10k_sdio_mbox_rx_packet, and then later manually
adjusted in ath10k_sdio_mbox_rx_process_packet.

The first problem is that ath10k_sdio_mbox_rx_process_packet does not
use proper skb_put commands to adjust the length (it directly changes
skb->len), so we end up with a mismatch between skb->head + skb->tail
and skb->data + skb->len. This is quite serious, 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).

Instead of re-adjusting the size in ath10k_sdio_mbox_rx_process_packet,
this moves the code to ath10k_sdio_mbox_rx_packet, and also add a
bounds check, as skb_put would crash the kernel if not enough space is
available.

Fixes: 8530b4e7b22bc3b ("ath10k: sdio: set skb len for all rx packets")
Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>

---

One simple way to reproduce this issue is this scriplet, that sends a
lot of small packets over SSH (it usually fails before reaching 300):
(for i in `seq 1 300`; do echo $i; sleep 0.1; done) | ssh $IP cat

I was not able to check the original use case why the code was added
(packets > 1500 bytes), as the FW on my board crashes when sending
such large packets.

 drivers/net/wireless/ath/ath10k/sdio.c | 25 +++++++++++++++++--------
 1 file changed, 17 insertions(+), 8 deletions(-)

diff --git a/drivers/net/wireless/ath/ath10k/sdio.c b/drivers/net/wireless/ath/ath10k/sdio.c
index 8ed4fbd8d6c3888..0a3ac44a13698c1 100644
--- a/drivers/net/wireless/ath/ath10k/sdio.c
+++ b/drivers/net/wireless/ath/ath10k/sdio.c
@@ -381,16 +381,11 @@ 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);
-
 	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);
 
@@ -636,9 +631,23 @@ 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);
+	if (!ret) {
+		/* Update actual length. The original length may be incorrect,
+		 * as the FW will bundle multiple packets as long as their sizes
+		 * fit within the same aligned length (pkt->alloc_len).
+		 */
+		struct ath10k_htc_hdr *htc_hdr =
+			(struct ath10k_htc_hdr *)skb->data;
+		pkt->act_len = le16_to_cpu(htc_hdr->len) + sizeof(*htc_hdr);
+		if (pkt->act_len <= pkt->alloc_len) {
+			skb_put(skb, pkt->act_len);
+		} else {
+			ath10k_warn(ar, "rx_packet too large (%d > %d)\n",
+				    pkt->act_len, pkt->alloc_len);
+			ret = -EMSGSIZE;
+		}
+	}
 	pkt->status = ret;
-	if (!ret)
-		skb_put(skb, pkt->act_len);
 
 	return ret;
 }
-- 
2.23.0.187.g17f5b7556c-goog