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smtpav03.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id DE74F5805A; Wed, 20 Sep 2023 20:37:50 +0000 (GMT) Received: from smtpav03.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 341C558056; Wed, 20 Sep 2023 20:37:50 +0000 (GMT) Received: from [9.47.158.152] (unknown [9.47.158.152]) by smtpav03.dal12v.mail.ibm.com (Postfix) with ESMTPS; Wed, 20 Sep 2023 20:37:50 +0000 (GMT) Message-ID: <8a65f5eb-2b59-9903-c6b8-84971f8765ae@linux.ibm.com> Date: Wed, 20 Sep 2023 16:37:49 -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: syzbot , amir73il@gmail.com, brauner@kernel.org, jlayton@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, zohar@linux.ibm.com, casey@schaufler-ca.com References: <000000000000259bd8060596e33f@google.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed X-TM-AS-GCONF: 00 X-Proofpoint-GUID: Kbc4INJMNgj4ReNRe8sxaQgKTckhzWu5 X-Proofpoint-ORIG-GUID: 8S0Dh3bbjUOU1Cc6xdcX6ucNZtaUTEIW Content-Transfer-Encoding: 8bit X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.267,Aquarius:18.0.980,Hydra:6.0.601,FMLib:17.11.176.26 definitions=2023-09-20_11,2023-09-20_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 mlxscore=0 adultscore=0 impostorscore=0 lowpriorityscore=0 mlxlogscore=317 suspectscore=0 clxscore=1015 bulkscore=0 malwarescore=0 spamscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2308100000 definitions=main-2309200172 Precedence: bulk List-ID: X-Mailing-List: linux-unionfs@vger.kernel.org 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.    Stefan