linux-kernel - Re: [syzbot] [maple-tree?] BUG: unable to handle kernel paging request in mas

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Date: Thu, 13 Jun 2024 15:02:14 -0400
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: syzbot <syzbot+c67d06ab25a9bc4adf35@...kaller.appspotmail.com>,
        akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, maple-tree@...ts.infradead.org,
        syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [maple-tree?] BUG: unable to handle kernel paging
 request in mas_walk

* Liam R. Howlett <Liam.Howlett@...cle.com> [240604 14:08]:
> * syzbot <syzbot+c67d06ab25a9bc4adf35@...kaller.appspotmail.com> [240603 22:23]:
> > Hello,
> > 
> > syzbot found the following issue on:
> > 
> > HEAD commit:    4a4be1ad3a6e Revert "vfs: Delete the associated dentry whe..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=128638ba980000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=bd6024aedb15e15c
> > dashboard link: https://syzkaller.appspot.com/bug?extid=c67d06ab25a9bc4adf35
> > compiler:       aarch64-linux-gnu-gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> > userspace arch: arm64
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=106f71aa980000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16b4ffc6980000
> > 
> > Downloadable assets:
> > disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/384ffdcca292/non_bootable_disk-4a4be1ad.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/75957361122b/vmlinux-4a4be1ad.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/6c766b0ec377/Image-4a4be1ad.gz.xz
> > 
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+c67d06ab25a9bc4adf35@...kaller.appspotmail.com
> > 
> > Unable to handle kernel paging request at virtual address 00700000077b9b78
> 
> I don't think the bot is testing my forced update of the tree, so I'll
> try again.
> 
> #sys test git://git.infradead.org/users/jedix/linux-maple.git syz_20240603_v2
> 
> This is a revert a some patches - which seems to stop all the crashing
> for me.
> 
> Looks to be the same as this [1] syzbot report.  All seem to be related
> to madvise and these patches are the last to modify the area (besides
> mseal() specifically calling out madvise, but that would not cause the
> issue).
> 
> The patches I revered also name arm64 as special.
> 
> [1] https://syzkaller.appspot.com/bug?extid=7eaa0d7b9fccf21052f1

This should be fixed in 6.10-rc3 because of the arm fix in the area I
suspected.  I have no way of verifying that since the bot decided to
stop responding.

This puts us in a difficult situation of needing to jump on bot bugs for
security concerns and wasting copious amounts of time chasing our own
tails.