usercopy: avoid potentially undefined behavior in pointer math
check_bogus_address() checked for pointer overflow using this expression,
where 'ptr' has type 'const void *':
ptr + n < ptr
Since pointer wraparound is undefined behavior, gcc at -O2 by default
treats it like the following, which would not behave as intended:
(long)n < 0
Fortunately, this doesn't currently happen for kernel code because kernel
code is compiled with -fno-strict-overflow. But the expression should be
fixed anyway to use well-defined integer arithmetic, since it could be
treated differently by different compilers in the future or could be
reported by tools checking for undefined behavior.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
diff --git a/mm/usercopy.c b/mm/usercopy.c
index 8ebae91..82f81df 100644
--- a/mm/usercopy.c
+++ b/mm/usercopy.c
@@ -124,7 +124,7 @@
static inline const char *check_bogus_address(const void *ptr, unsigned long n)
{
/* Reject if object wraps past end of memory. */
- if (ptr + n < ptr)
+ if ((unsigned long)ptr + n < (unsigned long)ptr)
return "<wrapped address>";
/* Reject if NULL or ZERO-allocation. */