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@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

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 53d6081f9e8b9bc4da356979e56e9cce7302f788..3e416a3cb66d415edeba51991a3df81a98f80b52 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';