libfdt: Fix segfault when calling fit_check_format() on corrupt FIT images

From: Jon Nalley <[email protected]>

It has been observed that fit_check_format() will fail when passed a corrupt FIT image. This was tracked down to _fdt_string_eq():
return (strlen(p) == len) && (memcmp(p, s, len) == 0);

In the case of a corrupt FIT image one can't depend on 'p' being NULL terminated. I changed it to use strnlen() to fix the issue.

---
Changes in v2:
- Pass len + 1, not len to strnlen as that's the best practice for strnlen.

---
 lib/libfdt/fdt_ro.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index f2154e8..36af043 100644
@@ -44,7 +44,7 @@ static int _fdt_string_eq(const void *fdt, int stroffset,
 {
 	const char *p = fdt_string(fdt, stroffset);
 
-	return (strlen(p) == len) && (memcmp(p, s, len) == 0);
+	return (strnlen(p, len + 1) == len) && (memcmp(p, s, len) == 0);
 }
 
 int fdt_get_mem_rsv(const void *fdt, int n, uint64_t *address, uint64_t *size)

1.7.9.5

Applied to u-boot/master, thanks!

Tom
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