Re: [syzbot] BUG: unable to handle kernel paging request in truncate_inode_partial_folio

[Mike Rapoport <rppt@kernel.org>]

On Fri, Jul 01, 2022 at 03:32:41PM +0800, Hillf Danton wrote:
> On Thu, 30 Jun 2022 11:47:39 +0300 Mike Rapoport wrote:
> > On Wed, Jun 29, 2022 at 09:30:12AM -0700, Axel Rasmussen wrote:
> > > On Tue, Jun 28, 2022 at 9:41 PM Eric Biggers <ebiggers@kernel.org> wrote:
> > 
> > >From edfcb2f0d31c2132bda483635dd2a8dd295efb04 Mon Sep 17 00:00:00 2001
> > From: Mike Rapoport <rppt@linux.ibm.com>
> > Date: Thu, 30 Jun 2022 11:26:37 +0300
> > Subject: [PATCH] secretmem: fix unhandled fault in truncate
> > 
> > syzkaller reports the following issue:
> > 
> > BUG: unable to handle page fault for address: ffff888021f7e005
> > PGD 11401067 P4D 11401067 PUD 11402067 PMD 21f7d063 PTE 800fffffde081060
> > Oops: 0002 [#1] PREEMPT SMP KASAN
> > CPU: 0 PID: 3761 Comm: syz-executor281 Not tainted 5.19.0-rc4-syzkaller-00014-g941e3e791269 #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> > RIP: 0010:memset_erms+0x9/0x10 arch/x86/lib/memset_64.S:64
> > Code: c1 e9 03 40 0f b6 f6 48 b8 01 01 01 01 01 01 01 01 48 0f af c6 f3 48 ab 89 d1 f3 aa 4c 89 c8 c3 90 49 89 f9 40 88 f0 48 89 d1 <f3> aa 4c 89 c8 c3 90 49 89 fa 40 0f b6 ce 48 b8 01 01 01 01 01 01
> > RSP: 0018:ffffc9000329fa90 EFLAGS: 00010202
> > RAX: 0000000000000000 RBX: 0000000000001000 RCX: 0000000000000ffb
> > RDX: 0000000000000ffb RSI: 0000000000000000 RDI: ffff888021f7e005
> > RBP: ffffea000087df80 R08: 0000000000000001 R09: ffff888021f7e005
> > R10: ffffed10043efdff R11: 0000000000000000 R12: 0000000000000005
> > R13: 0000000000000000 R14: 0000000000001000 R15: 0000000000000ffb
> > FS:  00007fb29d8b2700(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: ffff888021f7e005 CR3: 0000000026e7b000 CR4: 00000000003506f0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > Call Trace:
> >  <TASK>
> >  zero_user_segments include/linux/highmem.h:272 [inline]
> >  folio_zero_range include/linux/highmem.h:428 [inline]
> >  truncate_inode_partial_folio+0x76a/0xdf0 mm/truncate.c:237
> >  truncate_inode_pages_range+0x83b/0x1530 mm/truncate.c:381
> >  truncate_inode_pages mm/truncate.c:452 [inline]
> >  truncate_pagecache+0x63/0x90 mm/truncate.c:753
> >  simple_setattr+0xed/0x110 fs/libfs.c:535
> >  secretmem_setattr+0xae/0xf0 mm/secretmem.c:170
> >  notify_change+0xb8c/0x12b0 fs/attr.c:424
> >  do_truncate+0x13c/0x200 fs/open.c:65
> >  do_sys_ftruncate+0x536/0x730 fs/open.c:193
> >  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> >  do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
> >  entry_SYSCALL_64_after_hwframe+0x46/0xb0
> > RIP: 0033:0x7fb29d900899
> > Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 11 15 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
> > RSP: 002b:00007fb29d8b2318 EFLAGS: 00000246 ORIG_RAX: 000000000000004d
> > RAX: ffffffffffffffda RBX: 00007fb29d988408 RCX: 00007fb29d900899
> > RDX: 00007fb29d900899 RSI: 0000000000000005 RDI: 0000000000000003
> > RBP: 00007fb29d988400 R08: 0000000000000000 R09: 0000000000000000
> > R10: 0000000000000000 R11: 0000000000000246 R12: 00007fb29d98840c
> > R13: 00007ffca01a23bf R14: 00007fb29d8b2400 R15: 0000000000022000
> >  </TASK>
> > Modules linked in:
> > CR2: ffff888021f7e005
> > ---[ end trace 0000000000000000 ]---
> > 
> > Eric Biggers suggested that this happens when
> > secretmem_setattr()->simple_setattr() races with secretmem_fault() so
> > that a page that is faulted in by secretmem_fault() (and thus removed
> > from the direct map) is zeroed by inode truncation right afterwards.
> > 
> > Use an rw_semaphore to make secretmem_fault() and secretmem_setattr()
> > mutually exclusive.
> 
> Given inode_lock() in do_truncate(), another simpler option is to lock
> inode in the fault path if the suggested race is the root cause.

Yeah, it makes sense. It does not look like a race would happen anywhere
but do_truncate().
 
> Hillf
> 

-- 
Sincerely yours,
Mike.