netdev - Re: [PATCH] net: Work around crash in ipv6 fib-walk-continue

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Date:   Fri, 4 May 2018 10:57:30 -0700
From:   Ben Greear <greearb@...delatech.com>
To:     David Ahern <dsahern@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH] net: Work around crash in ipv6 fib-walk-continue

On 05/04/2018 10:47 AM, David Ahern wrote:
> On 4/19/18 12:01 PM, greearb@...delatech.com wrote:
>> From: Ben Greear <greearb@...delatech.com>
>>
>> This keeps us from crashing in certain test cases where we
>> bring up many (1000, for instance) mac-vlans with IPv6
>> enabled in the kernel.  This bug has been around for a
>> very long time.
>>
>> Until a real fix is found (and for stable), maybe it
>> is better to return an incomplete fib walk instead
>> of crashing.
>>
>> BUG: unable to handle kernel NULL pointer dereference at 8
>> IP: fib6_walk_continue+0x5b/0x140 [ipv6]
>> PGD 80000007dfc0c067 P4D 80000007dfc0c067 PUD 7e66ff067 PMD 0
>> Oops: 0000 [#1] PREEMPT SMP PTI
>> Modules linked in: nf_conntrack_netlink nf_conntrack nfnetlink nf_defrag_ipv4 libcrc32c vrf]
>> CPU: 3 PID: 15117 Comm: ip Tainted: G           O     4.16.0+ #5
>> Hardware name: Iron_Systems,Inc CS-CAD-2U-A02/X10SRL-F, BIOS 2.0b 05/02/2017
>> RIP: 0010:fib6_walk_continue+0x5b/0x140 [ipv6]
>> RSP: 0018:ffffc90008c3bc10 EFLAGS: 00010287
>> RAX: ffff88085ac45050 RBX: ffff8807e03008a0 RCX: 0000000000000000
>> RDX: 0000000000000000 RSI: ffffc90008c3bc48 RDI: ffffffff8232b240
>> RBP: ffff880819167600 R08: 0000000000000008 R09: ffff8807dff10071
>> R10: ffffc90008c3bbd0 R11: 0000000000000000 R12: ffff8807e03008a0
>> R13: 0000000000000002 R14: ffff8807e05744c8 R15: ffff8807e08ef000
>> FS:  00007f2f04342700(0000) GS:ffff88087fcc0000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 0000000000000008 CR3: 00000007e0556002 CR4: 00000000003606e0
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>> Call Trace:
>>  inet6_dump_fib+0x14b/0x2c0 [ipv6]
>>  netlink_dump+0x216/0x2a0
>>  netlink_recvmsg+0x254/0x400
>>  ? copy_msghdr_from_user+0xb5/0x110
>>  ___sys_recvmsg+0xe9/0x230
>>  ? find_held_lock+0x3b/0xb0
>>  ? __handle_mm_fault+0x617/0x1180
>>  ? __audit_syscall_entry+0xb3/0x110
>>  ? __sys_recvmsg+0x39/0x70
>>  __sys_recvmsg+0x39/0x70
>>  do_syscall_64+0x63/0x120
>>  entry_SYSCALL_64_after_hwframe+0x3d/0xa2
>> RIP: 0033:0x7f2f03a72030
>> RSP: 002b:00007fffab3de508 EFLAGS: 00000246 ORIG_RAX: 000000000000002f
>> RAX: ffffffffffffffda RBX: 00007fffab3e641c RCX: 00007f2f03a72030
>> RDX: 0000000000000000 RSI: 00007fffab3de570 RDI: 0000000000000004
>> RBP: 0000000000000000 R08: 0000000000007e6c R09: 00007fffab3e63a8
>> R10: 00007fffab3de5b0 R11: 0000000000000246 R12: 00007fffab3e6608
>> R13: 000000000066b460 R14: 0000000000007e6c R15: 0000000000000000
>> Code: 85 d2 74 17 f6 40 2a 04 74 11 8b 53 2c 85 d2 0f 84 d7 00 00 00 83 ea 01 89 53 2c c7 4
>> RIP: fib6_walk_continue+0x5b/0x140 [ipv6] RSP: ffffc90008c3bc10
>> CR2: 0000000000000008
>> ---[ end trace bd03458864eb266c ]---
>>
>> Signed-off-by: Ben Greear <greearb@...delatech.com>
>> ---
>>
>
> Does your use case that triggers this involve replacing routes? I just
> noticed the route delete code in fib6_add_rt2node does not have the
> 'Adjust walkers' code that is in fib6_del_route.
>
> Further, the adjust walkers code in fib6_del_route looks suspicious in
> its timing with route deletes. If you have a reliable reproducer we can
> try a few things with fib6_del_route and the walker code.

Yes, we replace routes, and yes we can reliably reproduce it and will
be happy to test patches.

Thanks,
Ben


-- 
Ben Greear <greearb@...delatech.com>
Candela Technologies Inc  http://www.candelatech.com