[PATCH net] net/packet: ignore timestamp bits when testing tx frame status

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

From: Willem de Bruijn <willemb@google.com>

Since the commit in Fixes, the tx completion handler writes the frame
status as TP_STATUS_AVAILABLE | ts, where ts can be
TP_STATUS_TS_SOFTWARE or TP_STATUS_TS_RAW_HARDWARE.

Two places compare a tx frame status to TP_STATUS_AVAILABLE for
equality, and so fail to detect such a released frame:

- tpacket_snd(), when packet_xmit() fails: the packet is silently
  dropped instead of an error being returned to the caller for retry.

- packet_poll(), on the tx ring head frame: the socket is not reported
  as writable.

Mask out the timestamp bits in both. In packet_lookup_frame(), only do
so when testing a tx ring frame for TP_STATUS_AVAILABLE.

Fixes: b9c32fb27170 ("packet: if hw/sw ts enabled in rx/tx ring, report which ts we got")
Signed-off-by: Willem de Bruijn <willemb@google.com>
---
 net/packet/af_packet.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 6ff16eef24f4..1cabe292ebb4 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -398,6 +398,10 @@ static inline struct page * __pure pgv_to_page(void *addr)
 	return virt_to_page(addr);
 }
 
+/* Timestamp bits that may be set in addition to the frame state */
+static const u32 tp_status_ts_mask = TP_STATUS_TS_SOFTWARE |
+				     TP_STATUS_TS_RAW_HARDWARE;
+
 static void __packet_set_status(struct packet_sock *po, void *frame, int status)
 {
 	union tpacket_uhdr h;
@@ -519,6 +523,7 @@ static void *packet_lookup_frame(const struct packet_sock *po,
 {
 	unsigned int pg_vec_pos, frame_offset;
 	union tpacket_uhdr h;
+	u32 mask = 0;
 
 	pg_vec_pos = position / rb->frames_per_block;
 	frame_offset = position % rb->frames_per_block;
@@ -526,7 +531,10 @@ static void *packet_lookup_frame(const struct packet_sock *po,
 	h.raw = rb->pg_vec[pg_vec_pos].buffer +
 		(frame_offset * rb->frame_size);
 
-	if (status != __packet_get_status(po, h.raw))
+	if (rb == &po->tx_ring && status == TP_STATUS_AVAILABLE)
+		mask = tp_status_ts_mask;
+
+	if (status != (__packet_get_status(po, h.raw) & ~mask))
 		return NULL;
 
 	return h.raw;
@@ -2948,7 +2956,7 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
 		if (unlikely(err != 0)) {
 			if (err > 0)
 				err = net_xmit_errno(err);
-			if (err && __packet_get_status(po, ph) ==
+			if (err && (__packet_get_status(po, ph) & ~tp_status_ts_mask) ==
 				   TP_STATUS_AVAILABLE) {
 				/* skb was destructed already */
 				skb = NULL;
-- 
2.56.0.rc1.315.gc6ed9934b7-goog