Messages in this thread | | | Subject | Re: [PATCH] mm/usercopy: Use memory range to be accessed for wraparound check | From | William Kucharski <> | Date | Wed, 14 Nov 2018 03:35:25 -0700 |
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> 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
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