Re: [PATCH] drivers/net/slip: prevent data alignment fault

[William Tambe <tambewilliam@gmail.com>]

Thanks, sending v2 of the patch that uses put_unaligned() here, and
get_unaligned().

William

On Mon, Oct 2, 2023 at 1:31 AM Paul Mackerras <paulus@ozlabs.org> wrote:
>
> On Sun, Oct 01, 2023 at 09:45:57PM -0500, William Tambe wrote:
> > >From 594e53fa4913b1cb6232dbcc73d905a94c0cae73 Mon Sep 17 00:00:00 2001
> > From: William Tambe <tambewilliam@gmail.com>
> > Date: Sun, 1 Oct 2023 21:38:15 -0500
> > Subject: [PATCH] drivers/net/slip: prevent data alignment fault
> >
> > Prevent data alignment fault on architectures which cannot
> > do unaligned memory access.
> > ---
> >  drivers/net/slip/slhc.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/net/slip/slhc.c b/drivers/net/slip/slhc.c
> > index ba93bab948e0..08fd570a6d40 100644
> > --- a/drivers/net/slip/slhc.c
> > +++ b/drivers/net/slip/slhc.c
> > @@ -459,8 +459,8 @@ slhc_compress(struct slcompress *comp, unsigned
> > char *icp, int isize,
> >          *cpp = ocp;
> >          *cp++ = changes;
> >      }
> > -    *(__sum16 *)cp = csum;
> > -    cp += 2;
> > +    *cp++ = (char)(csum&0xff);
> > +    *cp++ = (char)((csum>>8)&0xff);
>
> You just changed the meaning of the code on big-endian machines.
>
> I think it would be better to use put_unaligned() here, and
> get_unaligned() below.
>
> >  /* deltaS is now the size of the change section of the compressed header */
> >      memcpy(cp,new_seq,deltaS);    /* Write list of deltas */
> >      memcpy(cp+deltaS,icp+hlen,isize-hlen);
> > @@ -534,7 +534,7 @@ slhc_uncompress(struct slcompress *comp, unsigned
> > char *icp, int isize)
> >      thp = &cs->cs_tcp;
> >      ip = &cs->cs_ip;
> >
> > -    thp->check = *(__sum16 *)cp;
> > +    thp->check = (((__sum16)*cp)|(((__sum16)*(cp+1))<<8));
> >      cp += 2;
> >
> >      thp->psh = (changes & TCP_PUSH_BIT) ? 1 : 0;
> > --
> > 2.34.1
>
> Paul.