linux-kernel - Re: [PATCH] mm/slub: fix to return errno if kmalloc() fails

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Date:   Fri, 9 Sep 2022 22:21:41 +0200
From:   "Vlastimil Babka (SUSE)" <vbabka@...nel.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Muchun Song <muchun.song@...ux.dev>, Chao Yu <chao@...nel.org>,
        Linux MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, jaegeuk@...nel.org,
        Chao Yu <chao.yu@...o.com>, stable@...nel.org,
        syzbot+81684812ea68216e08c5@...kaller.appspotmail.com,
        David Rientjes <rientjes@...gle.com>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Christoph Lameter <cl@...ux.com>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>
Subject: Re: [PATCH] mm/slub: fix to return errno if kmalloc() fails

On 9/9/22 22:06, Matthew Wilcox wrote:
> On Thu, Sep 08, 2022 at 11:25:08PM +0200, Vlastimil Babka (SUSE) wrote:
>> > I tend to agree with you. A mount operation shouldn’t panic the
>> > kernel.
>> 
>> Hmm kmalloc(64) shouldn't normally due that due to the the underlying page
>> allocation falling into the "too small to fail" category, wonder if
>> syzkaller was doing anything special here?
> 
> Here's the repro:
> 
> https://syzkaller.appspot.com/x/repro.c?x=17cd7fa3080000
> 
> you can see it does:
> 
>   fd = open("/proc/thread-self/fail-nth", O_RDWR);
>   if (fd == -1)
>     exit(1);
>   char buf[16];
>   sprintf(buf, "%d", nth);
>   if (write(fd, buf, strlen(buf)) != (ssize_t)strlen(buf))
> 
> so this is the kind of stupid nitpicky bug that we shouldn't be
> reporting, let alone fixing, IMO.

Ah, thanks.

Well I'm ok with eventually removing all such BUG_ONs including what
Christophe Jaillet suggested, but it certainly isn't urgent nor deserves Cc:
stable then.