On Sun, Dec 23, 2018 at 11:30 AM Dmitry Vyukov <dvyu...@google.com> wrote: > > On Sun, Dec 23, 2018 at 10:57 AM Dmitry Vyukov <dvyu...@google.com> wrote: > > > > On Sun, Dec 23, 2018 at 8:37 AM Dmitry Vyukov <dvyu...@google.com> wrote: > > > > > > On Sat, Dec 22, 2018 at 8:07 PM Manfred Spraul <manf...@colorfullife.com> > > > wrote: > > > > > > > > Hi Dmitry, > > > > > > > > On 12/20/18 4:36 PM, Dmitry Vyukov wrote: > > > > > On Wed, Dec 19, 2018 at 10:04 AM Manfred Spraul > > > > > <manf...@colorfullife.com> wrote: > > > > >> Hello Dmitry, > > > > >> > > > > >> On 12/12/18 11:55 AM, Dmitry Vyukov wrote: > > > > >>> On Tue, Dec 11, 2018 at 9:23 PM syzbot > > > > >>> <syzbot+1145ec2e23165570c...@syzkaller.appspotmail.com> wrote: > > > > >>>> Hello, > > > > >>>> > > > > >>>> syzbot found the following crash on: > > > > >>>> > > > > >>>> HEAD commit: f5d582777bcb Merge branch 'for-linus' of > > > > >>>> git://git.kernel... > > > > >>>> git tree: upstream > > > > >>>> console output: > > > > >>>> https://syzkaller.appspot.com/x/log.txt?x=135bc547400000 > > > > >>>> kernel config: > > > > >>>> https://syzkaller.appspot.com/x/.config?x=c8970c89a0efbb23 > > > > >>>> dashboard link: > > > > >>>> https://syzkaller.appspot.com/bug?extid=1145ec2e23165570c3ac > > > > >>>> compiler: gcc (GCC) 8.0.1 20180413 (experimental) > > > > >>>> syz repro: > > > > >>>> https://syzkaller.appspot.com/x/repro.syz?x=16803afb400000 > > > > >>> +Manfred, this looks similar to the other few crashes related to > > > > >>> semget$private(0x0, 0x4000, 0x3f) that you looked at. > > > > >> I found one unexpected (incorrect?) locking, see the attached patch. > > > > >> > > > > >> But I doubt that this is the root cause of the crashes. > > > > > > > > > > But why? These one-off sporadic crashes reported by syzbot looks > > > > > exactly like a subtle race and your patch touches sem_exit_ns involved > > > > > in all reports. > > > > > So if you don't spot anything else, I would say close these 3 reports > > > > > with this patch (I see you already included Reported-by tags which is > > > > > great!) and then wait for syzbot reaction. Since we got 3 of them, if > > > > > it's still not fixed I would expect that syzbot will be able to > > > > > retrigger this later again. > > > > > > > > As I wrote, unless semop() is used, sma->use_global_lock is always 9 and > > > > nothing can happen. > > > > > > > > Every single-operation semop() reduces use_global_lock by one, i.e a > > > > single semop call as done here cannot trigger the bug: > > > > > > > > https://syzkaller.appspot.com/text?tag=ReproSyz&x=16803afb400000 > > > > > > It contains "repeat":true,"procs":6, which means that it run 6 > > > processes running this test in infinite loop. The last mark about > > > number of tests executed was: > > > 2018/12/11 18:38:02 executed programs: 2955 > > > > > > > But, one more finding: > > > > > > > > https://syzkaller.appspot.com/bug?extid=1145ec2e23165570c3ac > > > > > > > > https://syzkaller.appspot.com/text?tag=CrashLog&x=109ecf6e400000 > > > > > > > > The log file contain 1080 lines like these: > > > > > > > > > semget$private(..., 0x4003, ...) > > > > > > > > > > semget$private(..., 0x4006, ...) > > > > > > > > > > semget$private(..., 0x4007, ...) > > > > > > > > It ends up as kmalloc(128*0x400x), i.e. slightly more than 2 MB, an > > > > allocation in the 4 MB kmalloc buffer: > > > > > > > > > [ 1201.210245] kmalloc-4194304 4698112KB 4698112KB > > > > > > > > > i.e.: 1147 4 MB kmalloc blocks --> are we leaking nearly 100% of the > > > > semaphore arrays?? > > > > > > /\/\/\/\/\/\ > > > > > > Ha, this is definitely not healthy. > > > > I can reproduce this infinite memory consumption with the C program: > > https://gist.githubusercontent.com/dvyukov/03ec54b3429ade16fa07bf8b2379aff3/raw/ae4f654e279810de2505e8fa41b73dc1d77778e6/gistfile1.txt > > > > But this is working as intended, right? It just creates infinite > > number of large semaphore sets, which reasonably consumes infinite > > amount of memory. > > Except that it also violates the memcg bound and a process can have > > effectively unlimited amount of such "drum memory" in semaphores. > > > > > > > > > > > > This one looks similar: > > > > > > > > https://syzkaller.appspot.com/bug?extid=c92d3646e35bc5d1a909 > > > > > > > > except that the array sizes are mixed, and thus there are kmalloc-1M and > > > > kmalloc-2M as well. > > > > > > > > (and I did not count the number of semget calls) > > > > > > > > > > > > The test apps use unshare(CLONE_NEWNS) and unshare(CLONE_NEWIPC), > > > > correct? > > > > > > > > I.e. no CLONE_NEWUSER. > > > > > > > > https://github.com/google/syzkaller/blob/master/executor/common_linux.h#L1523 > > > > > > CLONE_NEWUSER is used on some instances as well: > > > https://github.com/google/syzkaller/blob/master/executor/common_linux.h#L1765 > > > This crash happened on 2 different instances and 1 of them uses > > > CLONE_NEWUSER and another does not. > > > If it's important because of CAP_ADMIN in IPC namespace, then all > > > instances should have it (instances that don't use NEWUSER are just > > > root). > > 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.