Re: [PATCH] mm/usercopy: Use memory range to be accessed for wraparound check

On Nov 13, 2018, at 5:51 PM, Isaac J. Manjarres isaacm@codeaurora.org wrote:

diff --git a/mm/usercopy.c b/mm/usercopy.c index 852eb4e..0293645 100644 --- a/mm/usercopy.c +++ b/mm/usercopy.c @@ -151,7 +151,7 @@ static inline void check_bogus_address(const unsigned long ptr, unsigned long n, bool to_user) { /* Reject if object wraps past end of memory. */

• if (ptr + n < ptr)

• if (ptr + (n - 1) < ptr) usercopy_abort("wrapped address", NULL, to_user, 0, ptr + n);

I'm being paranoid, but is it possible this routine could ever be passed "n" set to zero?

If so, it will erroneously abort indicating a wrapped address as (n - 1) wraps to ULONG_MAX.

Easily fixed via:

if ((n != 0) && (ptr + (n - 1) < ptr))

William Kucharski