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Subjectkernel BUG at kernel/cred.c:434!
Date
Hi.


syzkaller reported the following BUG:

[   73.146973] kernel BUG at kernel/cred.c:434!
[   73.150231] invalid opcode: 0000 [#1] SMP KASAN PTI
[   73.151928] CPU: 2 PID: 4058 Comm: syz-executor.6 Not tainted
5.1.0-rc4-00062-g2d06b235815e-dirty #2
[   73.155174] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS rel-1.12.1-0-ga5cab58e9a3f-prebuilt.qemu.org 04/01/2014
[   73.159798] RIP: 0010:commit_creds+0xadb/0xe50
[   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
[   73.167852] RSP: 0000:ffff88836e65f5d0 EFLAGS: 00010293
[   73.169636] RAX: ffff8883767b0000 RBX: ffff88837f111300 RCX:
ffffffff8124b5db
[   73.171962] RDX: 0000000000000000 RSI: ffffffff83c9b140 RDI:
ffff88837f111300
[   73.174310] RBP: ffff888376610400 R08: 0000000000000000 R09:
0000000000000004
[   73.176646] R10: 0000000000000001 R11: ffffed107c655acf R12:
ffff8883767b0000
[   73.178527] Process accounting resumed
[   73.179021] R13: ffff88837f111900 R14: ffff88837f111300 R15:
ffff8883767b0ac0
[   73.179029] FS:  00007f2d207f9700(0000) GS:ffff8883e3280000(0000)
knlGS:0000000000000000
[   73.179034] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   73.179039] CR2: 00007f1500bd36c0 CR3: 00000003df304003 CR4:
00000000000206e0
[   73.179047] Call Trace:
[   73.190461]  selinux_setprocattr+0x2ea/0x8f0
[   73.191925]  ? ptrace_parent_sid+0x530/0x530
[   73.193436]  ? proc_pid_attr_write+0x185/0x5a0
[   73.194967]  security_setprocattr+0xa1/0x100
[   73.196408]  proc_pid_attr_write+0x307/0x5a0
[   73.197869]  ? mem_read+0x40/0x40
[   73.199013]  __vfs_write+0x81/0x100
[   73.200222]  __kernel_write+0xf8/0x330
[   73.201562]  do_acct_process+0xca5/0x1340
[   73.202969]  ? __ia32_sys_acct+0x1e0/0x1e0
[   73.204498]  ? find_held_lock+0x2f/0x1e0
[   73.205857]  ? rcu_irq_exit+0xec/0x2c0
[   73.207160]  ? lock_downgrade+0x630/0x630
[   73.208541]  acct_pin_kill+0x63/0x150
[   73.209816]  pin_kill+0x16d/0x7c0
[   73.210934]  ? lockdep_hardirqs_on+0x5e0/0x5e0
[   73.212452]  ? xas_start+0x155/0x510
[   73.213705]  ? pin_insert+0x50/0x50
[   73.214903]  ? finish_wait+0x270/0x270
[   73.216213]  ? cpumask_next+0x57/0x90
[   73.217442]  ? mnt_pin_kill+0x68/0x1d0
[   73.218851]  mnt_pin_kill+0x68/0x1d0
[   73.220398]  cleanup_mnt+0x11b/0x150
[   73.221970]  task_work_run+0x136/0x1b0
[   73.223427]  do_exit+0x830/0x2ca0
[   73.224586]  ? trace_hardirqs_off+0x3b/0x180
[   73.226088]  ? mm_update_next_owner+0x6a0/0x6a0
[   73.227622]  ? find_held_lock+0x2f/0x1e0
[   73.228954]  ? get_signal+0x2cf/0x1c00
[   73.230236]  ? lock_downgrade+0x630/0x630
[   73.231628]  ? rwlock_bug.part.0+0x90/0x90
[   73.233020]  do_group_exit+0x106/0x2f0
[   73.234330]  get_signal+0x325/0x1c00
[   73.235571]  do_signal+0x97/0x1670
[   73.236739]  ? do_send_specific+0x12d/0x220
[   73.238213]  ? lock_downgrade+0x630/0x630
[   73.239566]  ? setup_sigcontext+0x820/0x820
[   73.240982]  ? check_kill_permission+0x4a/0x510
[   73.242509]  ? do_send_specific+0x156/0x220
[   73.243905]  ? do_tkill+0x1c4/0x260
[   73.245081]  ? do_send_specific+0x220/0x220
[   73.246514]  ? trace_hardirqs_on_thunk+0x1a/0x1c
[   73.248061]  ? exit_to_usermode_loop+0x97/0x1d0
[   73.249619]  exit_to_usermode_loop+0x108/0x1d0
[   73.251129]  do_syscall_64+0x461/0x580
[   73.252454]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
[   73.254219] RIP: 0033:0x462eb9
[   73.255327] Code: Bad RIP value.
[   73.256539] RSP: 002b:00007f2d207f8c58 EFLAGS: 00000246 ORIG_RAX:
00000000000000c8
[   73.259454] RAX: 0000000000000000 RBX: 000000000073bf00 RCX:
0000000000462eb9
[   73.262309] RDX: 0000000000000000 RSI: 000000000000001e RDI:
0000000000000005
[   73.265064] RBP: 0000000000000002 R08: 0000000000000000 R09:
0000000000000000
[   73.267774] R10: 0000000000000000 R11: 0000000000000246 R12:
00007f2d207f96bc
[   73.270546] R13: 00000000004c5509 R14: 00000000007042f0 R15:
00000000ffffffff
[   73.273542] Modules linked in:
[   73.274670] Dumping ftrace buffer:
[   73.275852]    (ftrace buffer empty)
[   73.277187] ---[ end trace dde36a95f458175d ]---
[   73.278834] RIP: 0010:commit_creds+0xadb/0xe50
[   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
[   73.287090] RSP: 0000:ffff88836e65f5d0 EFLAGS: 00010293
[   73.288917] RAX: ffff8883767b0000 RBX: ffff88837f111300 RCX:
ffffffff8124b5db
[   73.291390] RDX: 0000000000000000 RSI: ffffffff83c9b140 RDI:
ffff88837f111300
[   73.293864] RBP: ffff888376610400 R08: 0000000000000000 R09:
0000000000000004
[   73.296370] R10: 0000000000000001 R11: ffffed107c655acf R12:
ffff8883767b0000
[   73.299275] R13: ffff88837f111900 R14: ffff88837f111300 R15:
ffff8883767b0ac0
[   73.301351] Process accounting resumed
[   73.301822] FS:  00007f2d207f9700(0000) GS:ffff8883e3280000(0000)
knlGS:0000000000000000
[   73.301827] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   73.301832] CR2: 0000000000462e8f CR3: 0000000003a18002 CR4:
00000000000206e0
[   73.301850] Kernel panic - not syncing: Fatal exception
[   73.310719] Process accounting resumed
[   73.311515] Process accounting resumed
[   73.318916] Dumping ftrace buffer:
[   73.318921]    (ftrace buffer empty)
[   73.318945] Kernel Offset: disabled
[   73.328061] Rebooting in 10 seconds..


425 int commit_creds(struct cred *new)
426 {
427         struct task_struct *task = current;
428         const struct cred *old = task->real_cred;
429
430         kdebug("commit_creds(%p{%d,%d})", new,
431                atomic_read(&new->usage),
432                read_cred_subscribers(new));
433
434         BUG_ON(task->cred != old);  // BUG here


I find that the call chain which triggered the BUG is :

do_exit
    |-=> acct_process
    |    -=> do_acct_process
    |        -=> orig_cred = override_creds(file->f_cred); // cred =
ffff8883c1878900/real_cred = ffff8883c1878900
    |        -=>  if (file_start_write_trylock(file))
{__kernel_write(file, &ac, sizeof(acct_t), &pos);}
    |               -=> __kernel_write+0xf8/0x330
    |                    -=> __vfs_write+0x81/0x100
    |                           -=> proc_pid_attr_write+0x307/0x5a0
    |                                -=> security_setprocattr+0xa1/0x100
    | -=>selinux_setprocattr+0x2ea/0x8f0
    | -=>commit_creds+0xd97/0x1080  // cred =
ffff888379a79c00/real_cred = ffff888379a79c00
    |       -=> revert_creds(orig_cred);   // cred =
ffff8883c1878900/real_cred = ffff888379a79c00
    |-=> task_work_run
           -=> cleanup_mnt+0x11b/0x150
                -=> mnt_pin_kill+0x68/0x1d0
                    -=> pin_kill+0x16d/0x7c0
                    -=> acct_pin_kill+0x2e/0x100
                    -=> do_acct_process+0x1a0/0x1340
                          -=> override_creds+0x18a/0x1c0   // cred =
ffff8883c1878900/real_cred = ffff888379a79c00
                          -=>  if (file_start_write_trylock(file))
{__kernel_write(file, &ac, sizeof(acct_t), &pos);}
                                    -=>   ......
-=>commit_creds+0xd97/0x1080   // new = ffff888379a6bb00, cred =
ffff8883c1878900, real_ceed = ffff888379a79c00 BUG here
                          -=> 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,

        Cheng Jian.


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