linux-kernel - Re: [net-next PATCH v4 1/3] sysctl: refactor integer handling proc code

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Message-Id: <201002161544.33086.opurdila@ixiacom.com>
Date:	Tue, 16 Feb 2010 15:44:33 +0200
From:	Octavian Purdila <opurdila@...acom.com>
To:	Cong Wang <amwang@...hat.com>
Cc:	David Miller <davem@...emloft.net>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Linux Kernel Developers <linux-kernel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [net-next PATCH v4 1/3] sysctl: refactor integer handling proc code

On Tuesday 16 February 2010 15:09:51 you wrote:
> Octavian Purdila wrote:
> > On Tuesday 16 February 2010 10:41:07 you wrote:
> >>> +static int proc_skip_wspace(char __user **buf, size_t *size)
> >>> +{
> >>> +     char c;
> >>> +
> >>> +     while (*size) {
> >>> +             if (get_user(c, *buf))
> >>> +                     return -EFAULT;
> >>> +             if (!isspace(c))
> >>> +                     break;
> >>> +             (*size)--; (*buf)++;
> >>> +     }
> >>> +
> >>> +     return 0;
> >>> +}
> >>
> >> In lib/string.c we have skip_spaces(), I think we can use it
> >> here instead of inventing another one.
> >
> > I'm afraid we can't, skip_spaces does not accept userspace buffers.
> 
> Well, you need to use copy_from_user() before call it.
> 

And how much would you copy? You need to either use a stack buffer and do a 
loop copy or you would need to copy the whole userspace buffer which means we 
need to allocate a kernel buffer. I think its much cleaner the way is currently 
done.
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