Date:   Tue, 21 Jun 2022 14:03:30 +0000
From:   Liam Howlett <liam.howlett@...cle.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
CC:     syzbot <syzbot+58b51ac2b04e388ab7b0@...kaller.appspotmail.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "arve@...roid.com" <arve@...roid.com>,
        "brauner@...nel.org" <brauner@...nel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "hridya@...gle.com" <hridya@...gle.com>,
        "joel@...lfernandes.org" <joel@...lfernandes.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "maco@...roid.com" <maco@...roid.com>,
        "surenb@...gle.com" <surenb@...gle.com>,
        "syzkaller-bugs@...glegroups.com" <syzkaller-bugs@...glegroups.com>,
        "tkjos@...roid.com" <tkjos@...roid.com>,
        "willy@...radead.org" <willy@...radead.org>,
        "minchan@...nel.org" <minchan@...nel.org>
Subject: Re: [syzbot] kernel BUG in binder_alloc_deferred_release

* Dmitry Vyukov <dvyukov@...gle.com> [220621 03:23]:
> On Tue, 21 Jun 2022 at 04:08, Liam Howlett <liam.howlett@...cle.com> wrote:
> >
> > * syzbot <syzbot+58b51ac2b04e388ab7b0@...kaller.appspotmail.com> [220619 21:47]:
> > > Hello,
> > >
> > > syzbot found the following issue on:
> > >
> > > HEAD commit:    6012273897fe Add linux-next specific files for 20220615
> > > git tree:       linux-next
> > > console+strace: https://syzkaller.appspot.com/x/log.txt?x=16596feff00000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=b4154677977b1776
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=58b51ac2b04e388ab7b0
> > > 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=1024e510080000
> > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=113e407ff00000
> > >
> > > The issue was bisected to:
> > >
> > > commit 42086abba43463fbf495cb80173600284b4c4e8c
> > > Author: Liam R. Howlett <Liam.Howlett@...cle.com>
> > > Date:   Tue Jun 14 19:00:27 2022 +0000
> > >
> > >     mm: start tracking VMAs with maple tree
> > >
> > > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=10ef827ff00000
> > > final oops:     https://syzkaller.appspot.com/x/report.txt?x=12ef827ff00000
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=14ef827ff00000
> > >
> > > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> 
> Hi Liam,
> 
> Please also add the Reported-by tag.
> 
> \/\/\/\/\/\/\/\/\/\/\/\/\/\/

Thank you.

New patch attached.

> 
> > > Reported-by: syzbot+58b51ac2b04e388ab7b0@...kaller.appspotmail.com
> > > Fixes: 42086abba434 ("mm: start tracking VMAs with maple tree")
> > >
> > > ------------[ cut here ]------------
> > > kernel BUG at drivers/android/binder_alloc.c:820!
> > > invalid opcode: 0000 [#1] PREEMPT SMP KASAN
> > > CPU: 0 PID: 2934 Comm: kworker/0:3 Not tainted 5.19.0-rc2-next-20220615-syzkaller #0
> > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> > > Workqueue: events binder_deferred_func
> > > RIP: 0010:binder_alloc_deferred_release+0x602/0x780 drivers/android/binder_alloc.c:820
> > > Code: c6 80 16 c7 8a 48 c7 c7 80 b6 48 8d e8 57 86 05 fd 31 ff 89 c5 89 c6 e8 fc ba 5b fa 85 ed 74 c6 e9 78 57 55 02 e8 9e be 5b fa <0f> 0b c7 44 24 20 00 00 00 00 e9 27 ff ff ff e8 8a be 5b fa 48 89
> > > RSP: 0018:ffffc9000de07bc8 EFLAGS: 00010293
> > > RAX: 0000000000000000 RBX: ffff8880519971e0 RCX: 0000000000000000
> > > RDX: ffff888026b0d7c0 RSI: ffffffff871f04b2 RDI: ffff888051997270
> > > RBP: ffff888051997000 R08: 0000000000000000 R09: ffffffff8dbcac17
> > > R10: fffffbfff1b79582 R11: 0000000000000000 R12: ffff888147653c60
> > > R13: ffff8880519972d8 R14: ffff888147653d10 R15: dffffc0000000000
> > > FS:  0000000000000000(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000
> > > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > CR2: 00007f99ddec19c1 CR3: 0000000077a01000 CR4: 00000000003506f0
> > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > > Call Trace:
> > >  <TASK>
> > >  binder_free_proc drivers/android/binder.c:4766 [inline]
> >
> > ...
> >
> >
> > This task has alloc->vma set to a freed VMA.  What is happening is that
> > I've added an allocation later in the mmap_region() code which is being
> > failed by the fuzzer.  This failure means that the vma recorded in the
> > binder code via the call_mmap() is going to be freed in the
> > mmap_region() failure path, but the binder code does not know of the
> > failure.
> >
> > I was going to move my preallocation above the call_mmap() to avoid this
> > failure, but that will basically mask the issue(s) in binder.  There are
> > two other possibilities that could cause the same binder failure.  The
> > first being a rather unlikely arch_validate_flags() returning false.
> > The second is a successful merge of the allocated VMA
> > - also rare, but still possible.
> >
> > The code records a VMA to be used later and drops the mmap_lock.
> > Shouldn't it record the *address* and look up the VMA when it is needed
> > to avoid using a freed pointer?  There has been at least one other issue
> > with recording the VMA [1].
> >
> > Anyways, the attached patch fixes the issue I've exposed by saving the
> > start address and looking it up.  I've added lockdep checks for good
> > measures.  It fixes the reproduces from this email, but may need more
> > oversight.
> >
> >
> > 1. https://lore.kernel.org/lkml/20190301230606.8302-1-tkjos@google.com/
> >
> > Thanks,
> > Liam
> >
> > --
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> > To view this discussion on the web visit https://groups.google.com/d/msgid/syzkaller-bugs/20220621020814.sjszxp3uz43rka62%40revolver.

View attachment "0001-android-binder-Stop-saving-a-pointer-to-the-VMA.patch" of type "text/x-diff" (3802 bytes)

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