From afb919ff6ae38f797c162bf1c5d7b3d5abbd5e32 Mon Sep 17 00:00:00 2001
From: Jan Beulich <jbeulich@suse.com>
Date: Mon, 20 Apr 2026 12:26:25 +0200
Subject: [PATCH] ns16550: harden positional parsing

Advancing past a character without knowing whether that's the NUL char is
at risk of reading beyond the buffer.

Fixes: 25de1f692059 ("Allow arch-specific defaults to be specified for ns16550")
Reported-by: Kamil Frankowicz <kamil.frankowicz@cert.pl>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
master commit: 2c43b5611ffbe35611dd391c949f7cb15e1b29e7
master date: 2026-04-07 13:54:19 +0200
---
 xen/drivers/char/ns16550.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/xen/drivers/char/ns16550.c b/xen/drivers/char/ns16550.c
index 96e837afe8..1f95618cf6 100644
--- a/xen/drivers/char/ns16550.c
+++ b/xen/drivers/char/ns16550.c
@@ -1547,6 +1547,9 @@ static bool __init parse_positional(struct ns16550 *uart, char **str)
     {
         uart->data_bits = simple_strtoul(conf, &conf, 10);
 
+        if ( !*conf )
+            PARSE_ERR_RET("bad DPS setting");
+
         uart->parity = parse_parity_char(*conf);
 
         uart->stop_bits = simple_strtoul(conf + 1, &conf, 10);