linux-kernel - Re: [syzbot] WARNING in mbind

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Message-ID: <20230110152154.fpydtasxppz2bx3q@revolver>
Date:   Tue, 10 Jan 2023 15:22:01 +0000
From:   Liam Howlett <liam.howlett@...cle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     syzbot <syzbot+502859d610c661e56545@...kaller.appspotmail.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "syzkaller-bugs@...glegroups.com" <syzkaller-bugs@...glegroups.com>
Subject: Re: [syzbot] WARNING in mbind_range

* Andrew Morton <akpm@...ux-foundation.org> [230109 19:02]:
> On Mon, 09 Jan 2023 06:15:39 -0800 syzbot <syzbot+502859d610c661e56545@...kaller.appspotmail.com> wrote:
> 
> > syzbot has found a reproducer for the following issue on:
> > 
> > HEAD commit:    543b9b2fe10b Add linux-next specific files for 20230109
> > git tree:       linux-next
> 
> THanks.  Will you be performing a bisection?

No need, I see what I did wrong.

> 
> > console+strace: https://syzkaller.appspot.com/x/log.txt?x=12978216480000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=ceb6f70a080e19c3
> > dashboard link: https://syzkaller.appspot.com/bug?extid=502859d610c661e56545
> > compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=117fcc02480000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1396d7d6480000
> > 
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/22f2428ec2eb/disk-543b9b2f.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/6003c7af47cc/vmlinux-543b9b2f.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/ac9a6ad60347/bzImage-543b9b2f.xz
> > 
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+502859d610c661e56545@...kaller.appspotmail.com
> > 
> > ------------[ cut here ]------------
> > WARNING: CPU: 0 PID: 5072 at mm/mempolicy.c:797 mbind_range+0x5d2/0x760 mm/mempolicy.c:797
> 
> static int mbind_range(struct mm_struct *mm, unsigned long start,
> 		       unsigned long end, struct mempolicy *new_pol)
> {
> 	VMA_ITERATOR(vmi, mm, start);
> 	struct vm_area_struct *prev;
> 	struct vm_area_struct *vma;
> 	int err = 0;
> 	pgoff_t pgoff;
> 
> 	prev = vma_prev(&vmi);
> 	vma = vma_find(&vmi, end);
> 	if (WARN_ON(!vma))
> 		return 0;
> 
> Liam recently altered this code with "mempolicy: convert to vma iterator"?

Yes, thanks.  This helped a lot in seeing what I did here.

...

Thanks,
Liam