From: Marcelo Ricardo Leitner
> Sent: 16 September 2016 14:45
> To: David Laight
> Cc: 'Neil Horman'; linux-sctp@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH net] sctp: fix SSN comparision
>
> On Fri, Sep 16, 2016 at 10:40:47AM -0300, Marcelo Ricardo Leitner wrote:
> > On Fri, Sep 16, 2016 at 01:33:47PM +0000, David Laight wrote:
> > > > > -static inline int ADDIP_SERIAL_gte(__u16 s, __u16 t)
> > > > > +static inline int ADDIP_SERIAL_gte(__u32 s, __u32 t)
> > > > > {
> > > > > return ((s) == (t)) || (((t) - (s)) & ADDIP_SERIAL_SIGN_BIT);
> > > > > }
> > >
> > > Does gcc manage to compile that to (s32)((t) - (s)) <= 0 ?
> >
> > I have no idea but I have a patch in the works for updating it to this
> > form, to be more like time_after(). Will probably post it by next week.
>
> Just for reference, this should be it. Not realy tested yet.
>
> commit b52575533dfefa1908c7bbe35bde0fa8359dd1a3
> Author: Marcelo Ricardo Leitner <marcelo.leitner@xxxxxxxxx>
> Date: Tue Aug 9 14:45:35 2016 -0300
>
> sctp: improve how SSN, TSN and ASCONF serial are compared
>
> Make it similar to time_before() macros instead.
>
> This patch also removes SSN_lte as it is not used.
...
> +#define TSN_lte(a,b) \
> + (typecheck(__u32, a) && \
> + typecheck(__u32, b) && \
> + ((__s32)((a) - (b)) <= 0))
...
> + for (i = 0; i < blocks; ++i) {
> + if (TSN_lte((__u32)ntohs(frags[i].gab.start), (__u32)gap) &&
> + TSN_lte((__u32)gap, (__u32)ntohs(frags[i].gab.end)))
Those casts look decidedly dubious, messy at best.
I'm pretty sure you're not managing modulo 2^16 arithmetic either.
I think you want:
#define TSN_lte(a, b) ((__s16)((a) - (b)) <= 0)
If a and b are 16bit the subtract is always well defined.
David
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