Message-ID: <CAHC9VhS=izWYH7uaFcF9vre3GF06FitLXj0uUOKzMAwvq29OEw@mail.gmail.com>
Date: Mon, 4 Mar 2024 22:15:57 -0500
From: Paul Moore <paul@...l-moore.com>
To: Sam Sun <samsun1006219@...il.com>
Cc: Christian Göttsche <cgzones@...glemail.com>, 
	linux-kernel@...r.kernel.org, "xrivendell7@...il.com" <xrivendell7@...il.com>, 
	syzkaller@...glegroups.com, selinux@...r.kernel.org, omosnace@...hat.com
Subject: Re: [Bug] WARNING: zero-size vmalloc in sel_write_load

On Mon, Mar 4, 2024 at 9:32 PM Sam Sun <samsun1006219@...il.com> wrote:
> On Tue, Mar 5, 2024 at 4:45 AM Paul Moore <paul@...l-moore.com> wrote:
> > On Mon, Mar 4, 2024 at 3:11 PM Christian Göttsche
> > <cgzones@...glemail.com> wrote:
> > > On Mon, 4 Mar 2024 at 20:19, Paul Moore <paul@...l-moore.com> wrote:
> > > > On Mon, Mar 4, 2024 at 9:08 AM Sam Sun <samsun1006219@...ilcom> wrote:
> > > > >
> > > > > Dear developers and maintainers,
> > > > >
> > > > > We encountered a warning in function sel_write_load(). It is tested on
> > > > > kernel 6.8.0-rc7. Bug report is listed below.
> > > > >
> > > > > ```
> > > > > WARNING: CPU: 1 PID: 8109 at mm/vmalloc.c:3247
> > > > > __vmalloc_node_range+0x10a0/0x1490 mm/vmalloc.c:3247
> > > > > Modules linked in:
> > > > > CPU: 1 PID: 8109 Comm: syz-executor370 Not tainted 6.7.0-rc7 #1
> > > > > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
> > > > > RIP: 0010:__vmalloc_node_range+0x10a0/0x1490 mm/vmalloc.c:3247
> > > > > Code: 65 48 2b 04 25 28 00 00 00 0f 85 98 02 00 00 48 81 c4 70 01 00
> > > > > 00 4c 89 e0 5b 5d 41 5c 41 5d 41 5e 41 5f c3 e8 71 43 b7 ff 90 <0f> 0b
> > > > > 90 45 31 e4 eb a1 e8 63 43 b7 ff 48 8b 4c 24 40 31 f6 45 31
> > > > > RSP: 0018:ffffc90002adf9c0 EFLAGS: 00010293
> > > > > RAX: 0000000000000000 RBX: dffffc0000000000 RCX: ffffffff81cdc194
> > > > > RDX: ffff888022124ec0 RSI: ffffffff81cdd16f RDI: 0000000000000007
> > > > > RBP: 0000000000000000 R08: 0000000000000007 R09: 0000000000000000
> > > > > R10: 0000000000000000 R11: 0000000000000001 R12: ffff888107373a48
> > > > > R13: dffffc0000000000 R14: 0000000000000000 R15: ffffc90002adfec8
> > > > > FS:  00005555560953c0(0000) GS:ffff888135c00000(0000) knlGS:0000000000000000
> > > > > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > > > CR2: 0000000020000010 CR3: 000000010503d000 CR4: 0000000000750ef0
> > > > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > > > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > > > > PKRU: 55555554
> > > > > Call Trace:
> > > > >  <TASK>
> > > > >  __vmalloc_node mm/vmalloc.c:3385 [inline]
> > > > >  vmalloc+0x6b/0x80 mm/vmalloc.c:3418
> > > > >  sel_write_load+0x27f/0x19d0 security/selinux/selinuxfs.c:603
> > > > >  vfs_write+0x2a9/0xd80 fs/read_write.c:582
> > > > >  ksys_pwrite64 fs/read_write.c:699 [inline]
> > > > >  __do_sys_pwrite64 fs/read_write.c:709 [inline]
> > > > >  __se_sys_pwrite64 fs/read_write.c:706 [inline]
> > > > >  __x64_sys_pwrite64+0x1f3/0x250 fs/read_write.c:706
> > > > >  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> > > > >  do_syscall_64+0x40/0x110 arch/x86/entry/common.c:83
> > > > >  entry_SYSCALL_64_after_hwframe+0x63/0x6b
> > > > > RIP: 0033:0x7f40e7728f8d
> > > > > Code: 28 c3 e8 46 1e 00 00 66 0f 1f 44 00 00 f3 0f 1e fa 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:00007fff5bf39508 EFLAGS: 00000246 ORIG_RAX: 0000000000000012
> > > > > RAX: ffffffffffffffda RBX: 00007fff5bf39708 RCX: 00007f40e7728f8d
> > > > > RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
> > > > > RBP: 0000000000000001 R08: 0000000000000000 R09: 00007fff5bf39708
> > > > > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
> > > > > R13: 00007fff5bf396f8 R14: 00007f40e77a6530 R15: 0000000000000001
> > > > >  </TASK>
> > > > > ```
> > > > >
> > > > > The cause of this bug is that in sel_write_load(), parameter "count"
> > > > > is controlled by user, which could be zero. It is passed to vmalloc()
> > > > > as an argument.
> > > > >
> > > > > If you have any questions, please contact us.
> > > > > Reported by: Yue Sun <samsun1006219@...il.com>
> > > > > Reported by: xingwei lee <xrivendell7@...il.com>
> > > >
> > > > Everything appears to be working as expected, vmalloc() caught the
> > > > zero-length allocation request, emitted the warning, returned NULL to
> > > > sel_write_load(), and sel_write_load() handled the error condition
> > > > triggered by vmalloc(0) returning NULL.  Did you see any unexpected
> > > > behavior beyond this warning message above?
> > >
> > > Probably because kernel warnings should not be reachable from
> > > userspace ...
> >
> > My question was asking if the reporter was seeing any unexpected
> > behavior *beyond* the warning message.  I wanted to make sure they
> > weren't seeing anything else on their system that we should also take
> > into account.
>
> I didn't see any unexpected behavior beyond this warning message. You
> are right, everything appears to be working as expected. Like
> Christian said, I enabled kernel panic_on_warn config. I thought
> kernel warning was something worthy to report, but I was wrong. In
> future reports, I will check carefully to eliminate kernel warnings
> like "vmalloc zero" and "page size alloc too large" if they don't have
> unexpected behaviors. Sorry for wasting your time analyzing it, and
> thanks for pointing out my mistake!

Thanks for the quick reply, I just wanted to make sure there wasn't
some other bug that was also triggered by passing a 0 count value; I'm
glad to hear there isn't.  Regardless, there is likely some value in
protecting against 0 count/size values and I just posted a patch to do
just that (and some other misc cleanups to sel_write_load()).

-- 
paul-moore.com

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