Re: kernel BUG at kernel/cred.c:434!

[Casey Schaufler]

On 4/11/2019 11:21 PM, chengjian (D) wrote:

Added LSM and SELinux lists.


> Hi.
>
>
> syzkaller reported the following BUG:
>
> [ÂÂ 73.146973] kernel BUG at kernel/cred.c:434!
> [ÂÂ 73.150231] invalid opcode: 0000 [#1] SMP KASAN PTI
> [ÂÂ 73.151928] CPU: 2 PID: 4058 Comm: syz-executor.6 Not tainted 
> 5.1.0-rc4-00062-g2d06b235815e-dirty #2
> [ÂÂ 73.155174] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), 
> BIOS rel-1.12.1-0-ga5cab58e9a3f-prebuilt.qemu.org 04/01/2014
> [ÂÂ 73.159798] RIP: 0010:commit_creds+0xadb/0xe50
> [ÂÂ 73.161426] Code: 8b 5b 20 48 c1 ea 03 0f b6 04 02 84 c0 74 08 3c 
> 03 0f 8e 06 03 00 00 39 5d 20 0f 85 ff fa ff ff e9 0c fb ff ff e8 05 
> a2 25 00 <0f> 0b 48 c7 c7 80 56 c0 83 e8 95 22 b1 00 e8 f2 a1 25 00 0f 
> 0b 48
> [ÂÂ 73.167852] RSP: 0000:ffff88836e65f5d0 EFLAGS: 00010293
> [ÂÂ 73.169636] RAX: ffff8883767b0000 RBX: ffff88837f111300 RCX: 
> ffffffff8124b5db
> [ÂÂ 73.171962] RDX: 0000000000000000 RSI: ffffffff83c9b140 RDI: 
> ffff88837f111300
> [ÂÂ 73.174310] RBP: ffff888376610400 R08: 0000000000000000 R09: 
> 0000000000000004
> [ÂÂ 73.176646] R10: 0000000000000001 R11: ffffed107c655acf R12: 
> ffff8883767b0000
> [ÂÂ 73.178527] Process accounting resumed
> [ÂÂ 73.179021] R13: ffff88837f111900 R14: ffff88837f111300 R15: 
> ffff8883767b0ac0
> [ÂÂ 73.179029] FS:Â 00007f2d207f9700(0000) GS:ffff8883e3280000(0000) 
> knlGS:0000000000000000
> [ÂÂ 73.179034] CS:Â 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ÂÂ 73.179039] CR2: 00007f1500bd36c0 CR3: 00000003df304003 CR4: 
> 00000000000206e0
> [ÂÂ 73.179047] Call Trace:
> [ÂÂ 73.190461]Â selinux_setprocattr+0x2ea/0x8f0
> [ÂÂ 73.191925]Â ? ptrace_parent_sid+0x530/0x530
> [ÂÂ 73.193436]Â ? proc_pid_attr_write+0x185/0x5a0
> [ÂÂ 73.194967]Â security_setprocattr+0xa1/0x100
> [ÂÂ 73.196408]Â proc_pid_attr_write+0x307/0x5a0
> [ÂÂ 73.197869]Â ? mem_read+0x40/0x40
> [ÂÂ 73.199013]Â __vfs_write+0x81/0x100
> [ÂÂ 73.200222]Â __kernel_write+0xf8/0x330
> [ÂÂ 73.201562]Â do_acct_process+0xca5/0x1340
> [ÂÂ 73.202969]Â ? __ia32_sys_acct+0x1e0/0x1e0
> [ÂÂ 73.204498]Â ? find_held_lock+0x2f/0x1e0
> [ÂÂ 73.205857]Â ? rcu_irq_exit+0xec/0x2c0
> [ÂÂ 73.207160]Â ? lock_downgrade+0x630/0x630
> [ÂÂ 73.208541]Â acct_pin_kill+0x63/0x150
> [ÂÂ 73.209816]Â pin_kill+0x16d/0x7c0
> [ÂÂ 73.210934]Â ? lockdep_hardirqs_on+0x5e0/0x5e0
> [ÂÂ 73.212452]Â ? xas_start+0x155/0x510
> [ÂÂ 73.213705]Â ? pin_insert+0x50/0x50
> [ÂÂ 73.214903]Â ? finish_wait+0x270/0x270
> [ÂÂ 73.216213]Â ? cpumask_next+0x57/0x90
> [ÂÂ 73.217442]Â ? mnt_pin_kill+0x68/0x1d0
> [ÂÂ 73.218851]Â mnt_pin_kill+0x68/0x1d0
> [ÂÂ 73.220398]Â cleanup_mnt+0x11b/0x150
> [ÂÂ 73.221970]Â task_work_run+0x136/0x1b0
> [ÂÂ 73.223427]Â do_exit+0x830/0x2ca0
> [ÂÂ 73.224586]Â ? trace_hardirqs_off+0x3b/0x180
> [ÂÂ 73.226088]Â ? mm_update_next_owner+0x6a0/0x6a0
> [ÂÂ 73.227622]Â ? find_held_lock+0x2f/0x1e0
> [ÂÂ 73.228954]Â ? get_signal+0x2cf/0x1c00
> [ÂÂ 73.230236]Â ? lock_downgrade+0x630/0x630
> [ÂÂ 73.231628]Â ? rwlock_bug.part.0+0x90/0x90
> [ÂÂ 73.233020]Â do_group_exit+0x106/0x2f0
> [ÂÂ 73.234330]Â get_signal+0x325/0x1c00
> [ÂÂ 73.235571]Â do_signal+0x97/0x1670
> [ÂÂ 73.236739]Â ? do_send_specific+0x12d/0x220
> [ÂÂ 73.238213]Â ? lock_downgrade+0x630/0x630
> [ÂÂ 73.239566]Â ? setup_sigcontext+0x820/0x820
> [ÂÂ 73.240982]Â ? check_kill_permission+0x4a/0x510
> [ÂÂ 73.242509]Â ? do_send_specific+0x156/0x220
> [ÂÂ 73.243905]Â ? do_tkill+0x1c4/0x260
> [ÂÂ 73.245081]Â ? do_send_specific+0x220/0x220
> [ÂÂ 73.246514]Â ? trace_hardirqs_on_thunk+0x1a/0x1c
> [ÂÂ 73.248061]Â ? exit_to_usermode_loop+0x97/0x1d0
> [ÂÂ 73.249619]Â exit_to_usermode_loop+0x108/0x1d0
> [ÂÂ 73.251129]Â do_syscall_64+0x461/0x580
> [ÂÂ 73.252454]Â entry_SYSCALL_64_after_hwframe+0x49/0xbe
> [ÂÂ 73.254219] RIP: 0033:0x462eb9
> [ÂÂ 73.255327] Code: Bad RIP value.
> [ÂÂ 73.256539] RSP: 002b:00007f2d207f8c58 EFLAGS: 00000246 ORIG_RAX: 
> 00000000000000c8
> [ÂÂ 73.259454] RAX: 0000000000000000 RBX: 000000000073bf00 RCX: 
> 0000000000462eb9
> [ÂÂ 73.262309] RDX: 0000000000000000 RSI: 000000000000001e RDI: 
> 0000000000000005
> [ÂÂ 73.265064] RBP: 0000000000000002 R08: 0000000000000000 R09: 
> 0000000000000000
> [ÂÂ 73.267774] R10: 0000000000000000 R11: 0000000000000246 R12: 
> 00007f2d207f96bc
> [ÂÂ 73.270546] R13: 00000000004c5509 R14: 00000000007042f0 R15: 
> 00000000ffffffff
> [ÂÂ 73.273542] Modules linked in:
> [ÂÂ 73.274670] Dumping ftrace buffer:
> [ÂÂ 73.275852]ÂÂÂ (ftrace buffer empty)
> [ÂÂ 73.277187] ---[ end trace dde36a95f458175d ]---
> [ÂÂ 73.278834] RIP: 0010:commit_creds+0xadb/0xe50
> [ÂÂ 73.280549] Code: 8b 5b 20 48 c1 ea 03 0f b6 04 02 84 c0 74 08 3c 
> 03 0f 8e 06 03 00 00 39 5d 20 0f 85 ff fa ff ff e9 0c fb ff ff e8 05 
> a2 25 00 <0f> 0b 48 c7 c7 80 56 c0 83 e8 95 22 b1 00 e8 f2 a1 25 00 0f 
> 0b 48
> [ÂÂ 73.287090] RSP: 0000:ffff88836e65f5d0 EFLAGS: 00010293
> [ÂÂ 73.288917] RAX: ffff8883767b0000 RBX: ffff88837f111300 RCX: 
> ffffffff8124b5db
> [ÂÂ 73.291390] RDX: 0000000000000000 RSI: ffffffff83c9b140 RDI: 
> ffff88837f111300
> [ÂÂ 73.293864] RBP: ffff888376610400 R08: 0000000000000000 R09: 
> 0000000000000004
> [ÂÂ 73.296370] R10: 0000000000000001 R11: ffffed107c655acf R12: 
> ffff8883767b0000
> [ÂÂ 73.299275] R13: ffff88837f111900 R14: ffff88837f111300 R15: 
> ffff8883767b0ac0
> [ÂÂ 73.301351] Process accounting resumed
> [ÂÂ 73.301822] FS:Â 00007f2d207f9700(0000) GS:ffff8883e3280000(0000) 
> knlGS:0000000000000000
> [ÂÂ 73.301827] CS:Â 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ÂÂ 73.301832] CR2: 0000000000462e8f CR3: 0000000003a18002 CR4: 
> 00000000000206e0
> [ÂÂ 73.301850] Kernel panic - not syncing: Fatal exception
> [ÂÂ 73.310719] Process accounting resumed
> [ÂÂ 73.311515] Process accounting resumed
> [ÂÂ 73.318916] Dumping ftrace buffer:
> [ÂÂ 73.318921]ÂÂÂ (ftrace buffer empty)
> [ÂÂ 73.318945] Kernel Offset: disabled
> [ÂÂ 73.328061] Rebooting in 10 seconds..
>
>
> 425 int commit_creds(struct cred *new)
> 426 {
> 427ÂÂÂÂÂÂÂÂ struct task_struct *task = current;
> 428ÂÂÂÂÂÂÂÂ const struct cred *old = task->real_cred;
> 429
> 430ÂÂÂÂÂÂÂÂ kdebug("commit_creds(%p{%d,%d})", new,
> 431ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ atomic_read(&new->usage),
> 432ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ read_cred_subscribers(new));
> 433
> 434ÂÂÂÂÂÂÂÂ BUG_ON(task->cred != old);Â // BUG here
>
>
> I find that the call chain which triggered the BUG is :
>
> do_exit
> ÂÂÂ |-=> acct_process
> ÂÂÂ |ÂÂÂ -=> do_acct_process
> ÂÂÂ |ÂÂÂÂÂÂÂ -=> orig_cred = override_creds(file->f_cred); // cred = 
> ffff8883c1878900/real_cred = ffff8883c1878900
> ÂÂÂ |ÂÂÂÂÂÂÂ -=>Â if (file_start_write_trylock(file)) 
> {__kernel_write(file, &ac, sizeof(acct_t), &pos);}
> ÂÂÂ |ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ -=> __kernel_write+0xf8/0x330
> ÂÂÂ |ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ -=> __vfs_write+0x81/0x100
> ÂÂÂ |ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ -=> proc_pid_attr_write+0x307/0x5a0
> ÂÂÂ |ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ -=> security_setprocattr+0xa1/0x100
> ÂÂÂ | -=>selinux_setprocattr+0x2ea/0x8f0
> ÂÂÂ | -=>commit_creds+0xd97/0x1080Â // cred = 
> ffff888379a79c00/real_cred = ffff888379a79c00
> ÂÂÂ |ÂÂÂÂÂÂ -=> revert_creds(orig_cred);ÂÂ // cred = 
> ffff8883c1878900/real_cred = ffff888379a79c00
> ÂÂÂ |-=> task_work_run
> ÂÂÂÂÂÂÂÂÂÂ -=> cleanup_mnt+0x11b/0x150
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ -=> mnt_pin_kill+0x68/0x1d0
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ -=> pin_kill+0x16d/0x7c0
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ -=> acct_pin_kill+0x2e/0x100
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ -=> do_acct_process+0x1a0/0x1340
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ -=> override_creds+0x18a/0x1c0ÂÂ // cred = 
> ffff8883c1878900/real_cred = ffff888379a79c00
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ -=>Â if (file_start_write_trylock(file)) 
> {__kernel_write(file, &ac, sizeof(acct_t), &pos);}
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ -=>ÂÂ ...... 
> -=>commit_creds+0xd97/0x1080ÂÂ // new = ffff888379a6bb00, cred = 
> ffff8883c1878900, real_ceed = ffff888379a79c00 BUG here
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ -=> revert_creds(orig_cred);
>
>
> Syzkaller Report Testcase:
>
> cat crash.log
>
> 04:05:28 executing program 3:
> clone(0x24100, 0x0, 0x0, 0x0, 0x0)
> r0 = gettid()
> perf_event_open(&(0x7f00000000c0)={0x2, 0x70, 0x4, 0x2, 0x0, 0x0, 0x0, 
> 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 
> 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 
> 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, @perf_bp={0x0}}, 0x0, 
> 0xffffffffffffffff, 0xffffffffffffffff, 0x0)
> acct(&(0x7f0000000000)='./file0\x00')
> r1 = openat$smack_thread_current(0xffffffffffffff9c, 
> &(0x7f0000000000)='/proc/thread-self/attr/current\x00', 0x2, 0x0)
> fcntl$setown(r1, 0x8, r0)
> rt_tgsigqueueinfo(r0, r0, 0x1e, &(0x7f00000002c0))
> tkill(r0, 0x1e)
>
>
> Reproduce this BUG:
> ./syz-execprog -executor=./syz-executor -repeat=0 -procs=16 -cover=0 
> ./crash.log
>
>
> Can anyone help me ?
>
>
> Thanks,
>
> ÂÂÂÂÂÂÂ Cheng Jian.