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

[Paul Mackerras <paulus@ozlabs.org>]

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.