[Asterisk-code-review] main/udptl.c: correctly handle udptl sequence wrap around (...asterisk[17.0])

[George Joseph]

George Joseph has submitted this change and it was merged. ( https://gerrit.asterisk.org/c/asterisk/+/11649 )

Change subject: main/udptl.c: correctly handle udptl sequence wrap around
......................................................................

main/udptl.c: correctly handle udptl sequence wrap around

incorrect handling of UDPTL squence number wrap arounds causes
loss of packets every time the wrap around occurs

ASTERISK-28483 #close

Change-Id: I33caeb2bf13c574a1ebb81714b58907091d64234
---
M main/udptl.c
1 file changed, 18 insertions(+), 0 deletions(-)

Approvals:
  Kevin Harwell: Looks good to me, but someone else must approve; Verified
  George Joseph: Looks good to me, approved; Approved for Submit



diff --git a/main/udptl.c b/main/udptl.c
index 99a9c74..555ae69 100644
--- a/main/udptl.c
+++ b/main/udptl.c
@@ -405,6 +405,24 @@
 	seq_no = (buf[0] << 8) | buf[1];
 	ptr += 2;
 
+	/* UDPTL sequence numbers are 16 bit so after 0xFFFF comes
+	   0 which breaks all packet recovery logic.  To fix this
+	   if we see that next expected packet (rx_seq_no) is close
+	   to or beyond the wrap around limit & the received packet
+	   is still near zero, then we 'unwrap' the received seqno
+	   so it has the value it would have had.  After a 16
+	   packet grace period (there shouldn't be  more than
+	   that many recovery packets) we wrap the expected
+	   sequence number around and things can return back
+	   to normal */
+	if (seq_no < 0x000F && s->rx_seq_no > 0xFFF0) {
+		/* received seq_no has wrapped adjust it */
+		seq_no += 0x10000;
+	} else {
+		/* otherwise make sure expected rx_seq_no is properly wrapped */
+		s->rx_seq_no &= 0xFFFF;
+	}
+
 	/* Break out the primary packet */
 	if ((stat1 = decode_open_type(buf, len, &ptr, &ifp, &ifp_len)) != 0)
 		return -1;

-- 
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Gerrit-Project: asterisk
Gerrit-Branch: 17.0
Gerrit-Change-Id: I33caeb2bf13c574a1ebb81714b58907091d64234
Gerrit-Change-Number: 11649
Gerrit-PatchSet: 1
Gerrit-Owner: Torrey Searle <tsearle at gmail.com>
Gerrit-Reviewer: Friendly Automation
Gerrit-Reviewer: George Joseph <gjoseph at digium.com>
Gerrit-Reviewer: Kevin Harwell <kharwell at digium.com>
Gerrit-MessageType: merged
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