Re: [PATCH net] ipvlan: Dont Use skb->sk in ipvlan_process_v{4,6}_outbound

[Paolo Abeni]

On Sat, 2024-05-25 at 11:42 +0800, Yue Haibing wrote:
> Raw packet from PF_PACKET socket ontop of an IPv6-backed ipvlan device will
> hit WARN_ON_ONCE() in sk_mc_loop() through sch_direct_xmit() path.
> 
> WARNING: CPU: 2 PID: 0 at net/core/sock.c:775 sk_mc_loop+0x2d/0x70
> Modules linked in: sch_netem ipvlan rfkill cirrus drm_shmem_helper sg drm_kms_helper
> CPU: 2 PID: 0 Comm: swapper/2 Kdump: loaded Not tainted 6.9.0+ #279
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
> RIP: 0010:sk_mc_loop+0x2d/0x70
> Code: fa 0f 1f 44 00 00 65 0f b7 15 f7 96 a3 4f 31 c0 66 85 d2 75 26 48 85 ff 74 1c
> RSP: 0018:ffffa9584015cd78 EFLAGS: 00010212
> RAX: 0000000000000011 RBX: ffff91e585793e00 RCX: 0000000002c6a001
> RDX: 0000000000000000 RSI: 0000000000000040 RDI: ffff91e589c0f000
> RBP: ffff91e5855bd100 R08: 0000000000000000 R09: 3d00545216f43d00
> R10: ffff91e584fdcc50 R11: 00000060dd8616f4 R12: ffff91e58132d000
> R13: ffff91e584fdcc68 R14: ffff91e5869ce800 R15: ffff91e589c0f000
> FS:  0000000000000000(0000) GS:ffff91e898100000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f788f7c44c0 CR3: 0000000008e1a000 CR4: 00000000000006f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
> <IRQ>
>  ? __warn (kernel/panic.c:693)
>  ? sk_mc_loop (net/core/sock.c:760)
>  ? report_bug (lib/bug.c:201 lib/bug.c:219)
>  ? handle_bug (arch/x86/kernel/traps.c:239)
>  ? exc_invalid_op (arch/x86/kernel/traps.c:260 (discriminator 1))
>  ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:621)
>  ? sk_mc_loop (net/core/sock.c:760)
>  ip6_finish_output2 (net/ipv6/ip6_output.c:83 (discriminator 1))
>  ? nf_hook_slow (net/netfilter/core.c:626)
>  ip6_finish_output (net/ipv6/ip6_output.c:222)
>  ? __pfx_ip6_finish_output (net/ipv6/ip6_output.c:215)
>  ipvlan_xmit_mode_l3 (drivers/net/ipvlan/ipvlan_core.c:602) ipvlan
>  ipvlan_start_xmit (drivers/net/ipvlan/ipvlan_main.c:226) ipvlan
>  dev_hard_start_xmit (net/core/dev.c:3594)
>  sch_direct_xmit (net/sched/sch_generic.c:343)
>  __qdisc_run (net/sched/sch_generic.c:416)
>  net_tx_action (net/core/dev.c:5286)
>  handle_softirqs (kernel/softirq.c:555)
>  __irq_exit_rcu (kernel/softirq.c:589)
>  sysvec_apic_timer_interrupt (arch/x86/kernel/apic/apic.c:1043)
> 
> The warning triggers as this:
> packet_sendmsg
>    packet_snd //skb->sk is packet sk
>       __dev_queue_xmit
>          __dev_xmit_skb //q->enqueue is not NULL
>              __qdisc_run
>                sch_direct_xmit
>                  dev_hard_start_xmit
>                    ipvlan_start_xmit
>                       ipvlan_xmit_mode_l3 //l3 mode
>                         ipvlan_process_outbound //vepa flag
>                           ipvlan_process_v6_outbound
>                             ip6_local_out
>                                 __ip6_finish_output
>                                   ip6_finish_output2 //multicast packet
>                                     sk_mc_loop //sk->sk_family is AF_PACKET
> 
> Call ip{6}_local_out() with NULL sk in ipvlan as other tunnels to fix this.
> 
> Fixes: f60e5990d9c1 ("ipv6: protect skb->sk accesses from recursive dereference inside the stack")

The patch LGTM, but the above fixes tag looks incorrect, I think the
reproducer should splat even before such commit as the relevant warning
will be still there and should be still reachable.

Cheers,

Paolo