linux-kernel - Re: [PATCH v2] staging: erofs: keep corrupted fs from crashing kernel in erofs

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Date:   Fri, 15 Feb 2019 12:35:03 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     devel@...verdev.osuosl.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Miao Xie <miaoxie@...wei.com>, Chao Yu <chao@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, stable@...r.kernel.org,
        weidu.du@...wei.com, Al Viro <viro@...IV.linux.org.uk>,
        linux-erofs@...ts.ozlabs.org, Fang Wei <fangwei1@...wei.com>
Subject: Re: [PATCH v2] staging: erofs: keep corrupted fs from crashing
 kernel in erofs_namei()

On Fri, Feb 15, 2019 at 05:32:33PM +0800, Chao Yu wrote:
> On 2019/2/15 15:57, Dan Carpenter wrote:
> > On Fri, Feb 15, 2019 at 03:02:25PM +0800, Chao Yu wrote:
> >> On 2019/2/1 20:16, Gao Xiang wrote:
> >>> +	/*
> >>> +	 * on-disk error, let's only BUG_ON in the debugging mode.
> >>> +	 * otherwise, it will return 1 to just skip the invalid name
> >>> +	 * and go on (in consideration of the lookup performance).
> >>> +	 */
> >>> +	DBG_BUGON(qd->name > qd->end);
> >>
> >> qd->name == qd->end is not allowed as well?
> >>
> >> So will it be better to return directly here?
> >>
> >> 	if (unlikely(qd->name >= qd->end)) {
> >> 		DBG_BUGON(1);
> >> 		return 1;
> >> 	}
> > 
> > Please don't add likely/unlikely() annotations unless you have
> > benchmarked it and it makes a difference.
> 
> Well, it only occur for corrupted image, since the image is readonly, so it
> is really rare.

The likely/unlikely() annotations make the code harder to read.  It's
only worth it if it's is a speedup on a fast path.

regards,
dan carpenter