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 <jlayton@xxxxxxxxxx> > > > 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@xxxxxxxxxxxxxxxxxxxxxxxxx > > > 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: > > <TASK> > > 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@xxxxxxxxxxxxxx/ 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? Cheers, -- Jeff Layton <jlayton@xxxxxxxxxx>
