From ff9166c623704337bd6fe66fce2838d9768a6634 Mon Sep 17 00:00:00 2001
From: Daniel Starke <daniel.starke@siemens.com>
Date: Thu, 14 Apr 2022 02:42:25 -0700
Subject: [PATCH] tty: n_gsm: fix incorrect UA handling
Git-commit: ff9166c623704337bd6fe66fce2838d9768a6634
Patch-mainline: v5.18-rc5
References: git-fixes

n_gsm is based on the 3GPP 07.010 and its newer version is the 3GPP 27.010.
See https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=1516
The changes from 07.010 to 27.010 are non-functional. Therefore, I refer to
the newer 27.010 here. Chapter 5.4.4.2 states that any received unnumbered
acknowledgment (UA) with its poll/final (PF) bit set to 0 shall be
discarded. Currently, all UA frame are handled in the same way regardless
of the PF bit. This does not comply with the standard.
Remove the UA case in gsm_queue() to process only UA frames with PF bit set
to 1 to abide the standard.

Fixes: e1eaea46bb40 ("tty: n_gsm line discipline")
Cc: stable@vger.kernel.org
Signed-off-by: Daniel Starke <daniel.starke@siemens.com>
Link: https://lore.kernel.org/r/20220414094225.4527-20-daniel.starke@siemens.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/tty/n_gsm.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 15be4a235783..e440c7f6d20e 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -1865,7 +1865,6 @@ static void gsm_queue(struct gsm_mux *gsm)
 			}
 		}
 		break;
-	case UA:
 	case UA|PF:
 		if (cr == 0 || dlci == NULL)
 			break;
-- 
2.35.3