Hi Dmitry,
let's simplify the mail, otherwise noone can follow:
On 12/23/18 11:42 AM, Dmitry Vyukov wrote:
My naive attempts to re-reproduce this failed so far.
But I noticed that _all_ logs for these 3 crashes:
https://syzkaller.appspot.com/bug?extid=c92d3646e35bc5d1a909
https://syzkaller.appspot.com/bug?extid=1145ec2e23165570c3ac
https://syzkaller.appspot.com/bug?extid=9d8b6fa6ee7636f350c1
involve low memory conditions. My gut feeling says this is not a
coincidence. This is also probably the reason why all reproducers
create large sem sets. There must be some bad interaction between low
memory condition and semaphores/ipc namespaces.
Actually was able to reproduce this with a syzkaller program:
./syz-execprog -repeat=0 -procs=10 prog
...
kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 8788 Comm: syz-executor8 Not tainted 4.20.0-rc7+ #6
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
RIP: 0010:__list_del_entry_valid+0x7e/0x150 lib/list_debug.c:51
Code: ad de 4c 8b 26 49 39 c4 74 66 48 b8 00 02 00 00 00 00 ad de 48
89 da 48 39 c3 74 65 48 b8 00 00 00 00 00 fc ff df 48 c1 ea 03 <80> 3c
02 00 75 7b 48 8b 13 48 39 f2 75 57 49 8d 7c 24 08 48 b8 00
RSP: 0018:ffff88804faef210 EFLAGS: 00010a02
RAX: dffffc0000000000 RBX: f817edba555e1f00 RCX: ffffffff831bad5f
RDX: 1f02fdb74aabc3e0 RSI: ffff88801b8a0720 RDI: ffff88801b8a0728
RBP: ffff88804faef228 R08: fffff52001055401 R09: fffff52001055401
R10: 0000000000000001 R11: fffff52001055400 R12: ffff88802d52cc98
R13: ffff88801b8a0728 R14: ffff88801b8a0720 R15: dffffc0000000000
FS: 0000000000d24940(0000) GS:ffff88802d500000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000004bb580 CR3: 0000000011177005 CR4: 00000000003606e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
__list_del_entry include/linux/list.h:117 [inline]
list_del include/linux/list.h:125 [inline]
unlink_queue ipc/sem.c:786 [inline]
freeary+0xddb/0x1c90 ipc/sem.c:1164
free_ipcs+0xf0/0x160 ipc/namespace.c:112
sem_exit_ns+0x20/0x40 ipc/sem.c:237
free_ipc_ns ipc/namespace.c:120 [inline]
put_ipc_ns+0x55/0x160 ipc/namespace.c:152
free_nsproxy+0xc0/0x1f0 kernel/nsproxy.c:180
switch_task_namespaces+0xa5/0xc0 kernel/nsproxy.c:229
exit_task_namespaces+0x17/0x20 kernel/nsproxy.c:234
do_exit+0x19e5/0x27d0 kernel/exit.c:866
do_group_exit+0x151/0x410 kernel/exit.c:970
__do_sys_exit_group kernel/exit.c:981 [inline]
__se_sys_exit_group kernel/exit.c:979 [inline]
__x64_sys_exit_group+0x3e/0x50 kernel/exit.c:979
do_syscall_64+0x192/0x770 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4570e9
Code: 5d af fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48
89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d
01 f0 ff ff 0f 83 2b af fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffe35f12018 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00000000004570e9
RDX: 0000000000410540 RSI: 0000000000a34c00 RDI: 0000000000000045
RBP: 00000000004a43a4 R08: 000000000000000c R09: 0000000000000000
R10: 0000000000d24940 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000001 R14: 0000000000000000 R15: 0000000000000008
Modules linked in:
Dumping ftrace buffer:
(ftrace buffer empty)
---[ end trace 17829b0f00569a59 ]---
RIP: 0010:__list_del_entry_valid+0x7e/0x150 lib/list_debug.c:51
Code: ad de 4c 8b 26 49 39 c4 74 66 48 b8 00 02 00 00 00 00 ad de 48
89 da 48 39 c3 74 65 48 b8 00 00 00 00 00 fc ff df 48 c1 ea 03 <80> 3c
02 00 75 7b 48 8b 13 48 39 f2 75 57 49 8d 7c 24 08 48 b8 00
RSP: 0018:ffff88804faef210 EFLAGS: 00010a02
RAX: dffffc0000000000 RBX: f817edba555e1f00 RCX: ffffffff831bad5f
RDX: 1f02fdb74aabc3e0 RSI: ffff88801b8a0720 RDI: ffff88801b8a0728
RBP: ffff88804faef228 R08: fffff52001055401 R09: fffff52001055401
R10: 0000000000000001 R11: fffff52001055400 R12: ffff88802d52cc98
R13: ffff88801b8a0728 R14: ffff88801b8a0720 R15: dffffc0000000000
FS: 0000000000d24940(0000) GS:ffff88802d500000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000004bb580 CR3: 0000000011177005 CR4: 00000000003606e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
The prog is:
unshare(0x8020000)
semget$private(0x0, 0x4007, 0x0)
kernel is on 9105b8aa50c182371533fc97db64fc8f26f051b3
and again it involved lots of oom kills, the repro eats all memory, a
process getting killed, frees some memory and the process repeats.
Ok, thus the above program triggers two bugs:
- a huge memory leak with semaphore arrays
- under OOM pressure, an oops.
1) I can reproduce the memory leak, it happens all the time :-(
I must look what is wrong.
2) regarding the crash:
What differs under oom pressure?
- kvmalloc can fall back to vmalloc()
- the 2nd or 3rd of multiple allocations can fail, and that triggers a
rare codepath/race condition.
- rcu callback can happen earlier that expected
So far, I didn't notice anything unexpected :-(
--
Manfred
