linux-kernel - Re: [PATCH v4 4/9] epoll: Add implementation for epoll_ctl

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Message-ID: <20150311022310.GB1437@ad.nay.redhat.com>
Date:	Wed, 11 Mar 2015 10:23:10 +0800
From:	Fam Zheng <famz@...hat.com>
To:	Dan Rosenberg <dan.j.rosenberg@...il.com>
Cc:	linux-kernel@...r.kernel.org, famz@...hat.com
Subject: Re: [PATCH v4 4/9] epoll: Add implementation for epoll_ctl_batch

On Tue, 03/10 09:59, Dan Rosenberg wrote:
> On 03/09/2015 09:49 PM, Fam Zheng wrote:
> > +	if (!cmds || ncmds <= 0 || ncmds > EP_MAX_BATCH)
> > +		return -EINVAL;
> > +	cmd_size = sizeof(struct epoll_ctl_cmd) * ncmds;
> > +	/* TODO: optimize for small arguments like select/poll with a stack
> > +	 * allocated buffer */
> > +
> > +	kcmds = kmalloc(cmd_size, GFP_KERNEL);
> > +	if (!kcmds)
> > +		return -ENOMEM;
> You probably want to define EP_MAX_BATCH as some sane value much less
> than INT_MAX/(sizeof(struct epoll_ctl_cmd)). While this avoids the
> integer overflow from before, any user can cause the kernel to kmalloc
> up to INT_MAX bytes. Probably not a huge deal because it's freed at the
> end of the syscall, but generally not a great idea.
> 

Yeah, makes sense, any suggested value?

Thanks,
Fam
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