From: John Ogness <john.ogness@linutronix.de>
Date: Mon, 17 Jul 2023 19:46:01 +0000 (+0206)
Subject: kdb: Do not assume write() callback available
X-Git-Tag: v5.10.235~171
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=392d2826c5d7f4578619346a10a1f293ceea7827;p=thirdparty%2Fkernel%2Fstable.git

kdb: Do not assume write() callback available

commit 6d3e0d8cc63221dec670d0ee92ac57961581e975 upstream.

It is allowed for consoles to not provide a write() callback. For
example ttynull does this.

Check if a write() callback is available before using it.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20230717194607.145135-2-john.ogness@linutronix.de
Cc: Brian Norris <briannorris@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
index b28b8a5ef6381..1d016767179f5 100644
--- a/kernel/debug/kdb/kdb_io.c
+++ b/kernel/debug/kdb/kdb_io.c
@@ -577,6 +577,8 @@ static void kdb_msg_write(const char *msg, int msg_len)
 			continue;
 		if (c == dbg_io_ops->cons)
 			continue;
+		if (!c->write)
+			continue;
 		/*
 		 * Set oops_in_progress to encourage the console drivers to
 		 * disregard their internal spin locks: in the current calling