linux-kernel - Re: [syzbot] [mm?] BUG: Bad page map (8)

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Message-ID: <9e26dd3a-f983-4d54-b162-52a9938d0dcd@redhat.com>
Date: Fri, 19 Jul 2024 13:21:30 +0200
From: David Hildenbrand <david@...hat.com>
To: syzbot <syzbot+ec4b7d82bb051330f15a@...kaller.appspotmail.com>,
 akpm@...ux-foundation.org, hughd@...gle.com, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, syzkaller-bugs@...glegroups.com,
 Vivek Kasireddy <vivek.kasireddy@...el.com>
Subject: Re: [syzbot] [mm?] BUG: Bad page map (8)

On 19.07.24 00:51, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    4d145e3f830b Merge tag 'i2c-for-6.10-rc8' of git://git.ker..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=11321495980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=6b5a15443200e31
> dashboard link: https://syzkaller.appspot.com/bug?extid=ec4b7d82bb051330f15a
> 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=113e054e980000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1366ab85980000
> 

The reproducer involves udmabuf. I suspect it has to do with it.

But I'm curius, does the reproducer not trigger before 4d145e3f830b on 
mainliny?

Viveks changes are not upstream yet, but I can only speculate that we 
have some issue similar to the one we had with hugetlb: udmabuf doing 
things with memfd/shmem pages that it shouldn't do, because it doesn't 
"own" these pages.

"udmabuf: Use vmf_insert_pfn and VM_PFNMAP for handling mmap" might help.

-- 
Cheers,

David / dhildenb