linux-ext4 - Re: [syzbot] KASAN: use-after-free Read in ext4_xattr_set

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Message-ID: <CACT4Y+ZhCWZhrzt9bW-Q=munq9RC+eow8zCpJU1fzFiEGQa+6w@mail.gmail.com>
Date:   Tue, 29 Mar 2022 14:01:22 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Ritesh Harjani <ritesh.list@...il.com>
Cc:     syzbot <syzbot+4cb1e27475bf90a9b926@...kaller.appspotmail.com>,
        adilger.kernel@...ger.ca, cmaiolino@...hat.com,
        lczerner@...hat.com, linux-ext4@...r.kernel.org,
        linux-kernel@...r.kernel.org, sjc@...bot.com,
        syzkaller-bugs@...glegroups.com, tytso@....edu, wanjiabing@...o.com
Subject: Re: [syzbot] KASAN: use-after-free Read in ext4_xattr_set_entry (4)

On Tue, 29 Mar 2022 at 13:50, Ritesh Harjani <ritesh.list@...il.com> wrote:
>
> On 22/03/25 07:18AM, Dmitry Vyukov wrote:
> > On Wed, 23 Mar 2022 at 16:07, syzbot
> > <syzbot+4cb1e27475bf90a9b926@...kaller.appspotmail.com> wrote:
> > >
> > > syzbot suspects this issue was fixed by commit:
> > >
> > > commit 6e47a3cc68fc525428297a00524833361ebbb0e9
> > > Author: Lukas Czerner <lczerner@...hat.com>
> > > Date:   Wed Oct 27 14:18:52 2021 +0000
> > >
> > >     ext4: get rid of super block and sbi from handle_mount_ops()
> > >
> > > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=100bc10b700000
> > > start commit:   f8ad8187c3b5 fs/pipe: allow sendfile() to pipe again
> > > git tree:       upstream
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=96b123631a6700e9
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=4cb1e27475bf90a9b926
> > > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11131f94d00000
> > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15c3761b500000
> > >
> > > If the result looks correct, please mark the issue as fixed by replying with:
> > >
> > > #syz fix: ext4: get rid of super block and sbi from handle_mount_ops()
> > >
> > > For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> >
> > Looks reasonable:
> >
> > #syz fix: ext4: get rid of super block and sbi from handle_mount_ops()
>
> Sorry, I might have missed some discussion maybe.
> But why do we think that this patch could fix the reported bug?
> Because I see this patch from Lukas is a part of "ext4: new mount API
> conversion" patch series. This I guess has nothing to do with the reported call
> stack, no?
>
> Or am I missing anything?

Hi Ritesh,

It looked reasonable because the identified patch is in ext4 and the
bug is also in ext4 + the bisection log looked reasonable + there were
no other suggestions/corrections. In such a case it's better to close
the bug with at least some reasonable fix, then let it pile to
hundreds of other unclosed bugs and prevent reporting of new bugs.



> BUG: KASAN: use-after-free in ext4_xattr_set_entry+0x3151/0x3780 fs/ext4/xattr.c:1586
> Read of size 4 at addr ffff888030c00004 by task syz-executor392/11280
>
> CPU: 0 PID: 11280 Comm: syz-executor392 Not tainted 5.11.0-rc5-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:79 [inline]
>  dump_stack+0x107/0x163 lib/dump_stack.c:120
>  print_address_description.constprop.0.cold+0x5b/0x2f8 mm/kasan/report.c:230
>  __kasan_report mm/kasan/report.c:396 [inline]
>  kasan_report.cold+0x79/0xd5 mm/kasan/report.c:413
>  ext4_xattr_set_entry+0x3151/0x3780 fs/ext4/xattr.c:1586
>  ext4_xattr_ibody_set+0x78/0x2b0 fs/ext4/xattr.c:2224
>  ext4_xattr_set_handle+0x8f4/0x13e0 fs/ext4/xattr.c:2380
>  ext4_xattr_set+0x13a/0x340 fs/ext4/xattr.c:2493
>  __vfs_setxattr+0x10e/0x170 fs/xattr.c:177
>  __vfs_setxattr_noperm+0x11a/0x4c0 fs/xattr.c:208
>  __vfs_setxattr_locked+0x1bf/0x250 fs/xattr.c:266
>  vfs_setxattr+0x135/0x320 fs/xattr.c:291
>  setxattr+0x1ff/0x290 fs/xattr.c:553
>  path_setxattr+0x170/0x190 fs/xattr.c:572
>  __do_sys_setxattr fs/xattr.c:587 [inline]
>  __se_sys_setxattr fs/xattr.c:583 [inline]
>  __x64_sys_setxattr+0xc0/0x160 fs/xattr.c:583
>  do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>
>
> -ritesh