linux-kernel - Re: [PATCH 4/8] pipe: fix limit checking in pipe_set

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Message-ID: <20160819054818.GH17944@1wt.eu>
Date:   Fri, 19 Aug 2016 07:48:18 +0200
From:   Willy Tarreau <w@....eu>
To:     "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Vegard Nossum <vegard.nossum@...cle.com>, socketpair@...il.com,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Jens Axboe <axboe@...com>, Al Viro <viro@...iv.linux.org.uk>,
        linux-api@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/8] pipe: fix limit checking in pipe_set_size()

Hi Michael,

Since you're changing this code, it's probably worth swapping the size
check and capable() below to save a function call in the normal path :

On Fri, Aug 19, 2016 at 05:25:35PM +1200, Michael Kerrisk (man-pages) wrote:
> +	if (nr_pages > pipe->buffers) {
> +		if (!capable(CAP_SYS_RESOURCE) && size > pipe_max_size) {

=>		if (size > pipe_max_size && !capable(CAP_SYS_RESOURCE)) {

> +			ret = -EPERM;
> +			goto out_revert_acct;
> +		} else if ((too_many_pipe_buffers_hard(pipe->user) ||
> +				too_many_pipe_buffers_soft(pipe->user)) &&
> +				!capable(CAP_SYS_RESOURCE) &&
> +				!capable(CAP_SYS_ADMIN)) {
> +			ret = -EPERM;
> +			goto out_revert_acct;
> +		}
> +	}
(...)

Cheers,
Willy