vsprintf: Fix potential unaligned access

BugLink: https://bugs.launchpad.net/bugs/1969110
[ Upstream commit d75b26f880f60ead301e79ba0f4a635c5a60767f ]

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@linux.intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220127181233.72910-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
(cherry picked from commit 2305e3460b424342fd658d2e79f5b66aac3b0497)
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index d7ad44f2c8f5715552ca7e63a8a79aecdb995dce..ec07f6312445abd16f9f2e96fee830024e4d1992 100644 (file)
--- 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"
@@ -1771,7 +1772,7 @@ 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);
@@ -1779,21 +1780,22 @@ 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';