Re: + fix-compat-space-msg-size-limit-for-msgsnd-msgrcv.patch addedto -mm tree

[suzuki]

Arnd Bergmann wrote:
> On Tuesday 14 November 2006 00:58, akpm@xxxxxxxx wrote:
>
>
> > Subject: Fix compat space msg size limit for msgsnd/msgrcv
> > From: suzuki <suzuki@xxxxxxxxxxxxxxxxxx>
> >
> > Currently we allocate 64k space on the user stack and use it the msgbuf for
> > sys_{msgrcv,msgsnd} for compat and the results are later copied in user [by
> > copy_in_user].
> >
> > This patch introduces helper routines for sys_{msgrcv,msgsnd} which would
> > accept the pointer to msgbuf along with the msgp->mtext.  This avoids the
> > need to allocate the msgsize on the userspace (thus removing the size
> > limit) and the overhead of an extra copy_in_user().
> >
> > Signed-off-by: Suzuki K P <suzuki@xxxxxxxxxx>
> > Cc: Arnd Bergmann <arnd@xxxxxxxx>
> > Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> > Signed-off-by: Andrew Morton <akpm@xxxxxxxx>

> This patch is definitely a big step in the right direction here, but why 
> not go all the way and pass msgp->mtype to do_msgsnd/do_msgrcv as kernel
> data instead of a user space pointer? This way you can get rid of the
> compat_alloc_userspace entirely and save avoid doing an extra 
> put_user/get_user pair in the compat_ function.

I left it as such, inorder to avoid the future changes that may come in 
the struct msgbuf -if at all-, which would make us to pass every single 
field as a parameter to do_msgrcv/do_msgsnd.

thanks,

Suzuki
> 	Arnd <><

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