From 53e9e33ede37a247d926db5e4a9e56b55204e66c Mon Sep 17 00:00:00 2001
From: Kees Cook <keescook@chromium.org>
Date: Thu, 10 Aug 2023 22:45:32 -0700
Subject: [PATCH] printk: ringbuffer: Fix truncating buffer size min_t cast
Git-commit: 53e9e33ede37a247d926db5e4a9e56b55204e66c
Patch-mainline: v6.6-rc1
References: bsc#1215875
If an output buffer size exceeded U16_MAX, the min_t(u16, ...) cast in
copy_data() was causing writes to truncate. This manifested as output
bytes being skipped, seen as %NUL bytes in pstore dumps when the available
record size was larger than 65536. Fix the cast to no longer truncate
the calculation.
Cc: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: John Ogness <john.ogness@linutronix.de>
Reported-by: Vijay Balakrishna <vijayb@linux.microsoft.com>
Link: https://lore.kernel.org/lkml/d8bb1ec7-a4c5-43a2-9de0-9643a70b899f@linux.microsoft.com/
Fixes: b6cf8b3f3312 ("printk: add lockless ringbuffer")
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Tested-by: Vijay Balakrishna <vijayb@linux.microsoft.com>
Tested-by: Guilherme G. Piccoli <gpiccoli@igalia.com> # Steam Deck
Reviewed-by: Tyler Hicks (Microsoft) <code@tyhicks.com>
Tested-by: Tyler Hicks (Microsoft) <code@tyhicks.com>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20230811054528.never.165-kees@kernel.org
---
kernel/printk/printk_ringbuffer.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c
index 2dc4d5a1f1ff..fde338606ce8 100644
--- a/kernel/printk/printk_ringbuffer.c
+++ b/kernel/printk/printk_ringbuffer.c
@@ -1735,7 +1735,7 @@ static bool copy_data(struct prb_data_ring *data_ring,
if (!buf || !buf_size)
return true;
- data_size = min_t(u16, buf_size, len);
+ data_size = min_t(unsigned int, buf_size, len);
memcpy(&buf[0], data, data_size); /* LMM(copy_data:A) */
return true;
--
2.35.3