Re: mm: GPF in __insert_vmap_area

[Kees Cook]

On Sat, Sep 3, 2016 at 8:15 AM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
> Hello,
>
> While running syzkaller fuzzer I've got the following GPF:
>
> general protection fault: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> Modules linked in:
> CPU: 2 PID: 4268 Comm: syz-executor Not tainted 4.8.0-rc3-next-20160825+ #8
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> task: ffff88006a6527c0 task.stack: ffff880052630000
> RIP: 0010:[<ffffffff82e1ccd6>]  [<ffffffff82e1ccd6>]
> __list_add_valid+0x26/0xd0 lib/list_debug.c:23
> RSP: 0018:ffff880052637a18  EFLAGS: 00010202
> RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffc90001c87000
> RDX: 0000000000000001 RSI: ffff88001344cdb0 RDI: 0000000000000008
> RBP: ffff880052637a30 R08: 0000000000000001 R09: 0000000000000000
> R10: 0000000000000000 R11: ffffffff8a5deee0 R12: ffff88006cc47230
> R13: ffff88001344cdb0 R14: ffff88006cc47230 R15: 0000000000000000
> FS:  00007fbacc97e700(0000) GS:ffff88006d200000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020de7000 CR3: 000000003c4d2000 CR4: 00000000000006e0
> DR0: 000000000000001e DR1: 000000000000001e DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
> Stack:
>  ffff88006cc47200 ffff88001344cd98 ffff88006cc47200 ffff880052637a78
>  ffffffff817bc6d1 ffff88006cc47208 ffffed000d988e41 ffff88006cc47208
>  ffff88006cc3e680 ffffc900035b7000 ffffc900035a7000 ffff88006cc47200
> Call Trace:
>  [<     inline     >] __list_add_rcu include/linux/rculist.h:51
>  [<     inline     >] list_add_rcu include/linux/rculist.h:78
>  [<ffffffff817bc6d1>] __insert_vmap_area+0x1c1/0x3c0 mm/vmalloc.c:340
>  [<ffffffff817bf544>] alloc_vmap_area+0x614/0x890 mm/vmalloc.c:458
>  [<ffffffff817bf8a8>] __get_vm_area_node+0xe8/0x340 mm/vmalloc.c:1377
>  [<ffffffff817c332a>] __vmalloc_node_range+0xaa/0x6d0 mm/vmalloc.c:1687
>  [<     inline     >] __vmalloc_node mm/vmalloc.c:1736
>  [<ffffffff817c39ab>] __vmalloc+0x5b/0x70 mm/vmalloc.c:1742
>  [<ffffffff8166ae9c>] bpf_prog_alloc+0x3c/0x190 kernel/bpf/core.c:82
>  [<ffffffff85c40ba9>] bpf_prog_create_from_user+0xa9/0x2c0
> net/core/filter.c:1132
>  [<     inline     >] seccomp_prepare_filter kernel/seccomp.c:373
>  [<     inline     >] seccomp_prepare_user_filter kernel/seccomp.c:408
>  [<     inline     >] seccomp_set_mode_filter kernel/seccomp.c:737
>  [<ffffffff815d7687>] do_seccomp+0x317/0x1800 kernel/seccomp.c:787
>  [<ffffffff815d8f84>] prctl_set_seccomp+0x34/0x60 kernel/seccomp.c:830
>  [<     inline     >] SYSC_prctl kernel/sys.c:2157
>  [<ffffffff813ccf8f>] SyS_prctl+0x82f/0xc80 kernel/sys.c:2075
>  [<ffffffff86e10700>] entry_SYSCALL_64_fastpath+0x23/0xc1
> Code: 00 00 00 00 00 55 48 b8 00 00 00 00 00 fc ff df 48 89 e5 41 54
> 49 89 fc 48 8d 7a 08 53 48 89 d3 48 89 fa 48 83 ec 08 48 c1 ea 03 <80>
> 3c 02 00 75 7c 48 8b 53 08 48 39 f2 75 37 48 89 f2 48 b8 00
> RIP  [<ffffffff82e1ccd6>] __list_add_valid+0x26/0xd0 lib/list_debug.c:23
>  RSP <ffff880052637a18>
> ---[ end trace 983e625f02f00d9f ]---
> Kernel panic - not syncing: Fatal exception
>
> On commit 0f98f121e1670eaa2a2fbb675e07d6ba7f0e146f of linux-next.
> Unfortunately it is not reproducible.
> The crashing line is:
>         CHECK_DATA_CORRUPTION(next->prev != prev,
>
> It crashed on KASAN check at (%rax, %rdx), this address corresponds to
> next address = 0x8. So next was ~NULL.

Paul, the RCU torture tests passed with the CONFIG_DEBUG_LIST changes,
IIRC, yes? I'd love to rule out some kind of race condition between
the removal and add code for the checking.

Daniel, IIRC there was some talk about RCU and BPF? Am I remembering
that correctly? I'm having a hard time imagining how a list add could
fail (maybe a race between two adds)?

Hmmm

-Kees

-- 
Kees Cook
Nexus Security