[PATCH v4 1/2] vsprintf: Fix potential unaligned access

[PATCH v4 1/2] vsprintf: Fix potential unaligned access

[Andy Shevchenko]

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>
---
v4: no changes
 lib/vsprintf.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 61528094ec87..4e8f3e9acb99 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"
@@ -1762,7 +1763,7 @@ 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);
@@ -1770,21 +1771,22 @@ 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

[PATCH v4 2/2] vsprintf: Move space out of string literals in fourcc_string()

[Andy Shevchenko]

The literals "big-endian" and "little-endian" may be potentially
occurred in other places. Dropping space allows linker to
merge them by using only a single copy.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
---
v4: dropped stpcpy() use (Kees), replaced "compress" with merge (Nick)
 lib/vsprintf.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 4e8f3e9acb99..a1babe5e07d1 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1781,7 +1781,8 @@ char *fourcc_string(char *buf, char *end, const u32 *fourcc,
 		*p++ = isascii(c) && isprint(c) ? c : '.';
 	}
 
-	strcpy(p, orig & BIT(31) ? " big-endian" : " little-endian");
+	*p++ = ' ';
+	strcpy(p, orig & BIT(31) ? "big-endian" : "little-endian");
 	p += strlen(p);
 
 	*p++ = ' ';
-- 
2.34.1

Re: [PATCH v4 2/2] vsprintf: Move space out of string literals in fourcc_string()

[Petr Mladek]

On Thu 2022-01-27 20:12:33, Andy Shevchenko wrote:
> The literals "big-endian" and "little-endian" may be potentially
> occurred in other places. Dropping space allows linker to
> merge them by using only a single copy.
> 
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>

Reviewed-by: Petr Mladek <pmladek@suse.com>

Best Regards,
Petr

PS: I have vacation the following week and will have limited internet
    access. I am going to push this patchset after I am back
    unless there are some complains.
    

Re: [PATCH v4 1/2] vsprintf: Fix potential unaligned access

[Petr Mladek]

On Thu 2022-01-27 20:12:32, Andy Shevchenko wrote:
> 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>

Both patches have been committed into printk/linux.git,
branch for-5.18-vsprintf-fourcc-fixup .

Best Regards,
Petr