On Thu, 20 Jul 2023 at 21:04, Lorenz Bauer <lmb@xxxxxxxxxxxxx> wrote:
>
> Currently the bpf_sk_assign helper in tc BPF context refuses SO_REUSEPORT
> sockets. This means we can't use the helper to steer traffic to Envoy,
> which configures SO_REUSEPORT on its sockets. In turn, we're blocked
> from removing TPROXY from our setup.
>
> The reason that bpf_sk_assign refuses such sockets is that the
> bpf_sk_lookup helpers don't execute SK_REUSEPORT programs. Instead,
> one of the reuseport sockets is selected by hash. This could cause
> dispatch to the "wrong" socket:
>
> sk = bpf_sk_lookup_tcp(...) // select SO_REUSEPORT by hash
> bpf_sk_assign(skb, sk) // SK_REUSEPORT wasn't executed
>
> Fixing this isn't as simple as invoking SK_REUSEPORT from the lookup
> helpers unfortunately. In the tc context, L2 headers are at the start
> of the skb, while SK_REUSEPORT expects L3 headers instead.
>
> Instead, we execute the SK_REUSEPORT program when the assigned socket
> is pulled out of the skb, further up the stack. This creates some
> trickiness with regards to refcounting as bpf_sk_assign will put both
> refcounted and RCU freed sockets in skb->sk. reuseport sockets are RCU
> freed. We can infer that the sk_assigned socket is RCU freed if the
> reuseport lookup succeeds, but convincing yourself of this fact isn't
> straight forward. Therefore we defensively check refcounting on the
> sk_assign sock even though it's probably not required in practice.
>
> Fixes: 8e368dc72e86 ("bpf: Fix use of sk->sk_reuseport from sk_assign")
> Fixes: cf7fbe660f2d ("bpf: Add socket assign support")
> Co-developed-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> Cc: Joe Stringer <joe@xxxxxxxxx>
> Link: https://lore.kernel.org/bpf/CACAyw98+qycmpQzKupquhkxbvWK4OFyDuuLMBNROnfWMZxUWeA@xxxxxxxxxxxxxx/
> Reviewed-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
> Signed-off-by: Lorenz Bauer <lmb@xxxxxxxxxxxxx>
> ---
Hi Lorenz, Kuniyuki, Martin,
I am getting a KASAN (inline mode) splat on bpf-next when I run
./test_progs -t btf_skc_cls_ingress, and I bisected it to this commit:
9c02bec95954 ("bpf, net: Support SO_REUSEPORT sockets with bpf_sk_assign")
bash-5.2# ./test_progs -t btf_skc_cls_ingress
[ 51.611015] bpf_testmod: loading out-of-tree module taints kernel.
[ 51.611434] bpf_testmod: module verification failed: signature
and/or required key missing - tainting kernel
[ 51.809645] ==================================================================
[ 51.810085] BUG: KASAN: slab-out-of-bounds in tcp_v6_rcv+0x2d7d/0x3440
[ 51.810458] Read of size 2 at addr ffff8881053f038c by task test_progs/226
[ 51.810848]
[ 51.810955] CPU: 4 PID: 226 Comm: test_progs Tainted: G
OE 6.5.0-rc2-g9c02bec95954 #51
[ 51.811467] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS 1.16.2-2.fc39 04/01/2014
[ 51.811968] Call Trace:
[ 51.812118] <IRQ>
[ 51.812239] dump_stack_lvl+0x4a/0x80
[ 51.812452] print_report+0xcf/0x670
[ 51.812660] ? __pfx___lock_acquire+0x10/0x10
[ 51.812930] kasan_report+0xda/0x110
[ 51.813140] ? tcp_v6_rcv+0x2d7d/0x3440
[ 51.813363] ? tcp_v6_rcv+0x2d7d/0x3440
[ 51.813585] tcp_v6_rcv+0x2d7d/0x3440
[ 51.813808] ? __pfx_tcp_v6_rcv+0x10/0x10
[ 51.814051] ? __pfx_raw6_local_deliver+0x10/0x10
[ 51.814322] ? lock_acquire+0x18e/0x4b0
[ 51.814543] ? ip6_input_finish+0xda/0x240
[ 51.814783] ip6_protocol_deliver_rcu+0x12a/0x1310
[ 51.815067] ? find_held_lock+0x2d/0x110
[ 51.815293] ip6_input_finish+0x118/0x240
[ 51.815526] ? __pfx_lock_release+0x10/0x10
[ 51.815770] ip6_input+0xc4/0x300
[ 51.815972] ? __pfx_ip6_input+0x10/0x10
[ 51.816204] ? ip6_rcv_core+0x996/0x1990
[ 51.816431] ipv6_rcv+0x3bf/0x780
[ 51.816625] ? __pfx_ipv6_rcv+0x10/0x10
[ 51.816853] ? lock_acquire+0x18e/0x4b0
[ 51.817088] ? process_backlog+0x1d8/0x620
[ 51.817325] ? __pfx_ipv6_rcv+0x10/0x10
[ 51.817546] __netif_receive_skb_one_core+0x11a/0x1b0
[ 51.817837] ? __pfx___netif_receive_skb_one_core+0x10/0x10
[ 51.818166] ? mark_held_locks+0x94/0xe0
[ 51.818392] process_backlog+0xd3/0x620
[ 51.818614] __napi_poll.constprop.0+0xa3/0x540
[ 51.818890] net_rx_action+0x3b4/0xa80
[ 51.819113] ? __pfx_net_rx_action+0x10/0x10
[ 51.819365] ? reacquire_held_locks+0x490/0x4b0
[ 51.819631] __do_softirq+0x202/0x83f
[ 51.819852] ? __pfx___do_softirq+0x10/0x10
[ 51.820103] ? tick_nohz_stop_idle+0x19e/0x280
[ 51.820360] ? __dev_queue_xmit+0x818/0x2d50
[ 51.820608] do_softirq+0x47/0xa0
[ 51.820817] </IRQ>
[ 51.820954] <TASK>
[ 51.821080] __local_bh_enable_ip+0xf2/0x120
[ 51.821324] __dev_queue_xmit+0x83c/0x2d50
[ 51.821561] ? __pfx_mark_lock+0x10/0x10
[ 51.821795] ? __pfx___dev_queue_xmit+0x10/0x10
[ 51.822064] ? lock_acquire+0x18e/0x4b0
[ 51.822285] ? find_held_lock+0x2d/0x110
[ 51.822511] ? lock_release+0x1de/0x620
[ 51.822737] ? ip6_finish_output+0x666/0x1250
[ 51.822998] ? __pfx_lock_release+0x10/0x10
[ 51.823238] ? mark_held_locks+0x94/0xe0
[ 51.823467] ip6_finish_output2+0xd8d/0x1bb0
[ 51.823717] ? ip6_mtu+0x13f/0x350
[ 51.823928] ? __pfx_ip6_finish_output2+0x10/0x10
[ 51.824195] ? find_held_lock+0x2d/0x110
[ 51.824427] ? lock_release+0x1de/0x620
[ 51.824650] ip6_finish_output+0x666/0x1250
[ 51.824906] ip6_output+0x1ed/0x6c0
[ 51.825113] ? __pfx_ip6_output+0x10/0x10
[ 51.825343] ? ip6_xmit+0xed5/0x1f40
[ 51.825551] ? __pfx_ip6_finish_output+0x10/0x10
[ 51.825821] ? nf_hook_slow+0xa9/0x180
[ 51.826048] ip6_xmit+0xbd2/0x1f40
[ 51.826248] ? lock_acquire+0x181/0x4b0
[ 51.826470] ? __pfx_ip6_xmit+0x10/0x10
[ 51.826696] ? __pfx_dst_output+0x10/0x10
[ 51.826937] ? __pfx_lock_acquire+0x10/0x10
[ 51.827176] ? release_sock+0x53/0x180
[ 51.827393] ? __pfx_inet6_csk_route_socket+0x10/0x10
[ 51.827684] ? entry_SYSCALL_64_after_hwframe+0x6e/0xd8
[ 51.827993] inet6_csk_xmit+0x31c/0x570
[ 51.828215] ? __pfx_inet6_csk_xmit+0x10/0x10
[ 51.828467] __tcp_transmit_skb+0x1708/0x3630
[ 51.828732] ? __pfx___tcp_transmit_skb+0x10/0x10
[ 51.829017] ? __alloc_skb+0x110/0x280
[ 51.829238] ? __pfx___alloc_skb+0x10/0x10
[ 51.829474] ? __tcp_send_ack.part.0+0x64/0x590
[ 51.829743] tcp_rcv_state_process+0xeba/0x4ff0
[ 51.830015] ? __pfx_tcp_rcv_state_process+0x10/0x10
[ 51.830298] ? __pfx_mark_lock+0x10/0x10
[ 51.830524] ? find_held_lock+0x2d/0x110
[ 51.830756] ? lock_release+0x1de/0x620
[ 51.830988] ? __release_sock+0xd8/0x2b0
[ 51.831215] ? tcp_v6_do_rcv+0x34e/0x13a0
[ 51.831443] tcp_v6_do_rcv+0x34e/0x13a0
[ 51.831665] ? __local_bh_enable_ip+0xa6/0x120
[ 51.831935] __release_sock+0x12c/0x2b0
[ 51.832158] release_sock+0x53/0x180
[ 51.832365] __inet_stream_connect+0x6a2/0x1100
[ 51.832634] ? __pfx___inet_stream_connect+0x10/0x10
[ 51.832934] ? __pfx_woken_wake_function+0x10/0x10
[ 51.833209] ? lockdep_hardirqs_on_prepare+0x27b/0x3f0
[ 51.833501] inet_stream_connect+0x57/0xa0
[ 51.833743] __sys_connect+0x106/0x130
[ 51.833973] ? __sys_setsockopt+0x19d/0x410
[ 51.834211] ? __pfx___sys_connect+0x10/0x10
[ 51.834460] ? __pfx_blkcg_maybe_throttle_current+0x10/0x10
[ 51.834780] __x64_sys_connect+0x72/0xb0
[ 51.835019] ? syscall_enter_from_user_mode+0x20/0x50
[ 51.835312] do_syscall_64+0x3c/0x90
[ 51.835523] entry_SYSCALL_64_after_hwframe+0x6e/0xd8
[ 51.835818] RIP: 0033:0x7f99941965b4
[ 51.836034] Code: 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84
00 00 00 00 00 90 f3 0f 1e fa 80 3d b5 8d 12 00 00 74 13 b8 2a 00 00
00 0f 05 <48> 3d 00 f0 ff ff 77 4c c3 0f 1f 00 55 48 89 e5 48 83 ec 10
89 55
[ 51.837071] RSP: 002b:00007ffc9a4a3ea8 EFLAGS: 00000202 ORIG_RAX:
000000000000002a
[ 51.837507] RAX: ffffffffffffffda RBX: 00007ffc9a4a42a8 RCX: 00007f99941965b4
[ 51.837920] RDX: 000000000000001c RSI: 00007ffc9a4a3f10 RDI: 0000000000000008
[ 51.838318] RBP: 00007ffc9a4a3ee0 R08: 0000000000000010 R09: 0000000000000000
[ 51.838721] R10: 00007f999408a730 R11: 0000000000000202 R12: 0000000000000003
[ 51.839126] R13: 0000000000000000 R14: 00007f999433c000 R15: 0000000000ce2d90
[ 51.839527] </TASK>
[ 51.839658]
[ 51.839759] The buggy address belongs to the object at ffff8881053f0330
[ 51.839759] which belongs to the cache request_sock_TCPv6 of size 344
[ 51.840491] The buggy address is located 92 bytes inside of
[ 51.840491] allocated 344-byte region [ffff8881053f0330, ffff8881053f0488)
[ 51.841199]
[ 51.841298] The buggy address belongs to the physical page:
[ 51.841663] page:00000000e92b0bb6 refcount:1 mapcount:0
mapping:0000000000000000 index:0x0 pfn:0x1053f0
[ 51.842213] head:00000000e92b0bb6 order:1 entire_mapcount:0
nr_pages_mapped:0 pincount:0
[ 51.842741] flags:
0x2fffe0000010200(slab|head|node=0|zone=2|lastcpupid=0x7fff)
[ 51.843170] page_type: 0xffffffff()
[ 51.843374] raw: 02fffe0000010200 ffff8881016463c0 dead000000000122
0000000000000000
[ 51.843819] raw: 0000000000000000 0000000080140014 00000001ffffffff
0000000000000000
[ 51.844263] page dumped because: kasan: bad access detected
[ 51.844578]
[ 51.844691] Memory state around the buggy address:
[ 51.845125] ffff8881053f0280: fc fc fc fc fc fc fc fc fc fc fc fc
fc fc fc fc
[ 51.845599] ffff8881053f0300: fc fc fc fc fc fc fc fc fc fc fc fc
fc fc fc fc
[ 51.846069] >ffff8881053f0380: fc fc fc fc fc fc fc fc fc fc fc fc
fc fc fc fc
[ 51.846476]
^
[ 51.846684] ffff8881053f0400: fc fc fc fc fc fc fc fc fc fc fc fc
fc fc fc fc
[ 51.847109] ffff8881053f0480: fc fc fc fc fc fc fc fc fc fc fc fc
fc fc fc fc
[ 51.847526] ==================================================================
[ 51.847961] Disabling lock debugging due to kernel taint
#30/1 btf_skc_cls_ingress/conn:OK
#30/2 btf_skc_cls_ingress/syncookie:OK
#30 btf_skc_cls_ingress:OK
Summary: 1/2 PASSED, 0 SKIPPED, 0 FAILED
KASAN is pointing to this part of the commit:
0xffffffff8305164d is in tcp_v6_rcv (../include/net/inet6_hashtables.h:122).
117 return NULL;
118
119 if (!prefetched)
120 return sk;
121
122 if (sk->sk_protocol == IPPROTO_TCP) { // bad access
123 if (sk->sk_state != TCP_LISTEN)
124 return sk;
125 } else if (sk->sk_protocol == IPPROTO_UDP) {
Let me know if you have trouble reproducing or need any other information.
