From 7329a655875a2f4bd6984fe8a7e00a6981e802f3 Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Fri, 19 Aug 2016 12:15:22 -0700 Subject: 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 Signed-off-by: Kees Cook --- mm/usercopy.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'mm') diff --git a/mm/usercopy.c b/mm/usercopy.c index 8ebae91a6b55..82f81df2edcf 100644 --- a/mm/usercopy.c +++ b/mm/usercopy.c @@ -124,7 +124,7 @@ static inline const char *check_kernel_text_object(const void *ptr, 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 ""; /* Reject if NULL or ZERO-allocation. */ -- cgit v1.2.3