linux-kernel - [PATCH v1 1/1] vsprintf: Fix potential unaligned access

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Message-Id: <20220110205049.11696-1-andriy.shevchenko@linux.intel.com>
Date:   Mon, 10 Jan 2022 22:50:49 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Petr Mladek <pmladek@...e.com>, linux-kernel@...r.kernel.org
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>
Subject: [PATCH v1 1/1] vsprintf: Fix potential unaligned access

The %p4cc specifier in some cases might get an unaligned pointer.
Due to this we need to make copy to local variable once to avoid
potential crashes on some architectures due to improper access.

Fixes: af612e43de6d ("lib/vsprintf: Add support for printing V4L2 and DRM fourccs")
Cc: Sakari Ailus <sakari.ailus@...ux.intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
---
 lib/vsprintf.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index c130dcaca5e2..b02f01366acb 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -49,6 +49,7 @@
 
 #include <asm/page.h>		/* for PAGE_SIZE */
 #include <asm/byteorder.h>	/* cpu_to_le16 */
+#include <asm/unaligned.h>
 
 #include <linux/string_helpers.h>
 #include "kstrtox.h"
@@ -1761,7 +1762,7 @@ char *fourcc_string(char *buf, char *end, const u32 *fourcc,
 	char output[sizeof("0123 little-endian (0x01234567)")];
 	char *p = output;
 	unsigned int i;
-	u32 val;
+	u32 orig, val;
 
 	if (fmt[1] != 'c' || fmt[2] != 'c')
 		return error_string(buf, end, "(%p4?)", spec);
@@ -1769,21 +1770,22 @@ char *fourcc_string(char *buf, char *end, const u32 *fourcc,
 	if (check_pointer(&buf, end, fourcc, spec))
 		return buf;
 
-	val = *fourcc & ~BIT(31);
+	orig = get_unaligned(fourcc);
+	val = orig & ~BIT(31);
 
-	for (i = 0; i < sizeof(*fourcc); i++) {
+	for (i = 0; i < sizeof(u32); i++) {
 		unsigned char c = val >> (i * 8);
 
 		/* Print non-control ASCII characters as-is, dot otherwise */
 		*p++ = isascii(c) && isprint(c) ? c : '.';
 	}
 
-	strcpy(p, *fourcc & BIT(31) ? " big-endian" : " little-endian");
+	strcpy(p, orig & BIT(31) ? " big-endian" : " little-endian");
 	p += strlen(p);
 
 	*p++ = ' ';
 	*p++ = '(';
-	p = special_hex_number(p, output + sizeof(output) - 2, *fourcc, sizeof(u32));
+	p = special_hex_number(p, output + sizeof(output) - 2, orig, sizeof(u32));
 	*p++ = ')';
 	*p = '\0';
 
-- 
2.34.1