diff options
| author | Eric Biggers <ebiggers@google.com> | 2016-08-19 12:15:22 -0700 |
|---|---|---|
| committer | Kees Cook <keescook@chromium.org> | 2016-08-22 19:07:55 -0700 |
| commit | 7329a655875a2f4bd6984fe8a7e00a6981e802f3 (patch) | |
| tree | 5c77614be62600da9d02d3b57709280e91e7292d | |
| parent | ef0e1ea8856bed6ff8394d3dfe77f2cab487ecea (diff) | |
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>
| -rw-r--r-- | mm/usercopy.c | 2 |
1 files changed, 1 insertions, 1 deletions
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 "<wrapped address>"; /* Reject if NULL or ZERO-allocation. */ |