linux-hardening - [PATCH] um: refactor deprecated strncpy to strtomem

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Date:   Mon, 07 Aug 2023 21:17:56 +0000
From:   Justin Stitt <justinstitt@...gle.com>
To:     Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Johannes Berg <johannes@...solutions.net>
Cc:     linux-hardening@...r.kernel.org, linux-um@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH] um: refactor deprecated strncpy to strtomem

Use `strtomem` here since `console_buf` is not expected to be
NUL-terminated. We should probably also just use `MCONSOLE_MAX_DATA`
instead of using `ARRAY_SIZE()` for every iteration of the loop.

Also mark char buffer as `__nonstring` as per Kees' suggestion here [1]

Finally, follow checkpatch's recommendation of using `min_t` over `min`

Link: https://github.com/KSPP/linux/issues/90 [1]
Cc: linux-hardening@...r.kernel.org
Signed-off-by: Justin Stitt <justinstitt@...gle.com>
---
Notes:
I only build tested this patch.
---
 arch/um/drivers/mconsole_kern.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/um/drivers/mconsole_kern.c b/arch/um/drivers/mconsole_kern.c
index 5026e7b9adfe..fd4c024202ae 100644
--- a/arch/um/drivers/mconsole_kern.c
+++ b/arch/um/drivers/mconsole_kern.c
@@ -4,6 +4,7 @@
  * Copyright (C) 2001 - 2008 Jeff Dike (jdike@...dtoit,linux.intel}.com)
  */
 
+#include "linux/compiler_attributes.h"
 #include <linux/console.h>
 #include <linux/ctype.h>
 #include <linux/string.h>
@@ -554,7 +555,7 @@ struct mconsole_output {
 
 static DEFINE_SPINLOCK(client_lock);
 static LIST_HEAD(clients);
-static char console_buf[MCONSOLE_MAX_DATA];
+static char console_buf[MCONSOLE_MAX_DATA] __nonstring;
 
 static void console_write(struct console *console, const char *string,
 			  unsigned int len)
@@ -566,8 +567,8 @@ static void console_write(struct console *console, const char *string,
 		return;
 
 	while (len > 0) {
-		n = min((size_t) len, ARRAY_SIZE(console_buf));
-		strncpy(console_buf, string, n);
+		n = min_t(size_t, len, MCONSOLE_MAX_DATA);
+		strtomem(console_buf, string);
 		string += n;
 		len -= n;
 

---
base-commit: c1a515d3c0270628df8ae5f5118ba859b85464a2
change-id: 20230807-arch-um-3ef24413427e

Best regards,
--
Justin Stitt <justinstitt@...gle.com>