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smtpav03.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 0949158056; Thu, 21 Sep 2023 00:10:47 +0000 (GMT) Received: from smtpav03.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 4234D5803F; Thu, 21 Sep 2023 00:10:46 +0000 (GMT) Received: from [9.47.158.152] (unknown [9.47.158.152]) by smtpav03.dal12v.mail.ibm.com (Postfix) with ESMTPS; Thu, 21 Sep 2023 00:10:46 +0000 (GMT) Message-ID: <00dbd1e7-dfc8-86bc-536f-264a929ebb35@linux.ibm.com> Date: Wed, 20 Sep 2023 20:10:45 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [syzbot] [integrity] [overlayfs] general protection fault in d_path Content-Language: en-US From: Stefan Berger To: Jeff Layton , syzbot , amir73il@gmail.com, brauner@kernel.org, linux-fsdevel@vger.kernel.org, linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org, linux-unionfs@vger.kernel.org, miklos@szeredi.hu, syzkaller-bugs@googlegroups.com, 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X-Mailing-List: linux-fsdevel@vger.kernel.org On 9/20/23 18:09, Stefan Berger wrote: > > On 9/20/23 17:16, Jeff Layton wrote: >> On Wed, 2023-09-20 at 16:37 -0400, Stefan Berger wrote: >>> On 9/20/23 13:01, Stefan Berger wrote: >>>> On 9/17/23 20:04, syzbot wrote: >>>>> syzbot has bisected this issue to: >>>>> >>>>> commit db1d1e8b9867aae5c3e61ad7859abfcc4a6fd6c7 >>>>> Author: Jeff Layton >>>>> Date:   Mon Apr 17 16:55:51 2023 +0000 >>>>> >>>>>       IMA: use vfs_getattr_nosec to get the i_version >>>>> >>>>> bisection log: >>>>> https://syzkaller.appspot.com/x/bisect.txt?x=106f7e54680000 >>>>> start commit:   a747acc0b752 Merge tag 'linux-kselftest-next-6.6-rc2' >>>>> of g.. >>>>> git tree:       upstream >>>>> final oops: >>>>> https://syzkaller.appspot.com/x/report.txt?x=126f7e54680000 >>>>> console output: >>>>> https://syzkaller.appspot.com/x/log.txt?x=146f7e54680000 >>>>> kernel config: >>>>> https://syzkaller.appspot.com/x/.config?x=df91a3034fe3f122 >>>>> dashboard link: >>>>> https://syzkaller.appspot.com/bug?extid=a67fc5321ffb4b311c98 >>>>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1671b694680000 >>>>> C reproducer: >>>>> https://syzkaller.appspot.com/x/repro.c?x=14ec94d8680000 >>>>> >>>>> Reported-by: syzbot+a67fc5321ffb4b311c98@syzkaller.appspotmail.com >>>>> Fixes: db1d1e8b9867 ("IMA: use vfs_getattr_nosec to get the >>>>> i_version") >>>>> >>>>> For information about bisection process see: >>>>> https://goo.gl/tpsmEJ#bisection >>>> The final oops shows this here: >>>> >>>> BUG: kernel NULL pointer dereference, address: 0000000000000058 >>>> #PF: supervisor read access in kernel mode >>>> #PF: error_code(0x0000) - not-present page >>>> PGD 0 P4D 0 >>>> Oops: 0000 [#1] PREEMPT SMP >>>> CPU: 0 PID: 3192 Comm: syz-executor.0 Not tainted >>>> 6.4.0-rc2-syzkaller #0 >>>> Hardware name: Google Google Compute Engine/Google Compute Engine, >>>> BIOS Google 08/04/2023 >>>> RIP: 0010:__lock_acquire+0x35/0x490 kernel/locking/lockdep.c:4946 >>>> Code: 83 ec 18 65 4c 8b 35 aa 60 f4 7e 83 3d b7 11 e4 02 00 0f 84 05 >>>> 02 00 00 4c 89 cb 89 cd 41 89 d5 49 89 ff 83 fe 01 77 0c 89 f0 <49> 8b >>>> 44 c7 08 48 85 c0 75 1b 4c 89 ff 31 d2 45 89 c4 e8 74 f6 ff >>>> RSP: 0018:ffffc90002edb840 EFLAGS: 00010097 >>>> RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000002 >>>> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000050 >>>> RBP: 0000000000000002 R08: 0000000000000001 R09: 0000000000000000 >>>> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000 >>>> R13: 0000000000000000 R14: ffff888102ea5340 R15: 0000000000000050 >>>> FS:  0000000000000000(0000) GS:ffff88813bc00000(0000) >>>> knlGS:0000000000000000 >>>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >>>> CR2: 0000000000000058 CR3: 0000000003aa8000 CR4: 00000000003506f0 >>>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 >>>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 >>>> Call Trace: >>>>    >>>>   lock_acquire+0xd8/0x1f0 kernel/locking/lockdep.c:5691 >>>>   seqcount_lockdep_reader_access include/linux/seqlock.h:102 [inline] >>>>   get_fs_root_rcu fs/d_path.c:243 [inline] >>>>   d_path+0xd1/0x1f0 fs/d_path.c:285 >>>>   audit_log_d_path+0x65/0x130 kernel/audit.c:2139 >>>>   dump_common_audit_data security/lsm_audit.c:224 [inline] >>>>   common_lsm_audit+0x3b3/0x840 security/lsm_audit.c:458 >>>>   smack_log+0xad/0x130 security/smack/smack_access.c:383 >>>>   smk_tskacc+0xb1/0xd0 security/smack/smack_access.c:253 >>>>   smack_inode_getattr+0x8a/0xb0 security/smack/smack_lsm.c:1187 >>>>   security_inode_getattr+0x32/0x50 security/security.c:2114 >>>>   vfs_getattr+0x1b/0x40 fs/stat.c:167 >>>>   ovl_getattr+0xa6/0x3e0 fs/overlayfs/inode.c:173 >>>>   ima_check_last_writer security/integrity/ima/ima_main.c:171 [inline] >>>>   ima_file_free+0xbd/0x130 security/integrity/ima/ima_main.c:203 >>>>   __fput+0xc7/0x220 fs/file_table.c:315 >>>>   task_work_run+0x7d/0xa0 kernel/task_work.c:179 >>>>   exit_task_work include/linux/task_work.h:38 [inline] >>>>   do_exit+0x2c7/0xa80 kernel/exit.c:871 <----------------------- >>>>   do_group_exit+0x85/0xa0 kernel/exit.c:1021 >>>>   get_signal+0x73c/0x7f0 kernel/signal.c:2874 >>>>   arch_do_signal_or_restart+0x89/0x290 arch/x86/kernel/signal.c:306 >>>>   exit_to_user_mode_loop+0x61/0xb0 kernel/entry/common.c:168 >>>>   exit_to_user_mode_prepare+0x64/0xb0 kernel/entry/common.c:204 >>>>   __syscall_exit_to_user_mode_work kernel/entry/common.c:286 [inline] >>>>   syscall_exit_to_user_mode+0x2b/0x1d0 kernel/entry/common.c:297 >>>>   do_syscall_64+0x4d/0x90 arch/x86/entry/common.c:86 >>>>   entry_SYSCALL_64_after_hwframe+0x63/0xcd >>>> >>>> >>>> do_exit has called exit_fs(tsk) [ >>>> https://elixir.bootlin.com/linux/v6.4-rc2/source/kernel/exit.c#L867 ] >>>> >>>> exit_fs(tsk) has set tsk->fs = NULL [ >>>> https://elixir.bootlin.com/linux/v6.4-rc2/source/fs/fs_struct.c#L103 ] >>>> >>>> I think this then bites in d_path() where it calls: >>>> >>>>      get_fs_root_rcu(current->fs, &root);   [ >>>> https://elixir.bootlin.com/linux/v6.4-rc2/source/fs/d_path.c#L285 ] >>>> >>>> current->fs is likely NULL here. >>>> >>>> If this was correct it would have nothing to do with the actual patch, >>>> though, but rather with the fact that smack logs on process >>>> termination. I am not sure what the solution would be other than >>>> testing for current->fs == NULL in d_path before using it and >>>> returning an error that is not normally returned or trying to >>>> intercept this case in smack. >>> I have now been able to recreate the syzbot issue with the test program >>> and the issue is exactly the one described here, current->fs == NULL. >>> >> Earlier in this thread, Amir had a diagnosis that IMA is inappropriately >> trying to use f_path directly instead of using the helpers that are >> friendly for stacking filesystems. >> >> https://lore.kernel.org/linux-fsdevel/CAOQ4uxgjnYyeQL-LbS5kQ7+C0d6sjzKqMDWAtZW8cAkPaed6=Q@mail.gmail.com/ >> >> >> I'm not an IMA hacker so I'm not planning to roll a fix here. Perhaps >> someone on the IMA team could try this approach? > > > I have applied this patch here from Amir now and it does NOT resolve > the issue: > > https://lore.kernel.org/linux-integrity/296dae962a2a488bde682d3def074db91686e1c3.camel@linux.ibm.com/T/#m4ebdb780bf6952e7f210c55e87950d0cfa1d5eb0 > > This seems to resolve the issue: diff --git a/security/smack/smack_access.c b/security/smack/smack_access.c index 585e5e35710b..57afcea1e39b 100644 --- a/security/smack/smack_access.c +++ b/security/smack/smack_access.c @@ -347,6 +347,9 @@ void smack_log(char *subject_label, char *object_label, int request,         struct smack_audit_data *sad;         struct common_audit_data *a = &ad->a; +       if (current->flags & PF_EXITING) +               return; +         /* check if we have to log the current event */         if (result < 0 && (log_policy & SMACK_AUDIT_DENIED) == 0)                 return;