Re: [PATCH net-net] tun: Assign missing bpf_net_context.

From: Breno Leitao
Date: Thu Sep 12 2024 - 08:08:33 EST

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Hello Sebastian, Jakub,

On Wed, Jul 03, 2024 at 12:01:43PM -0700, Jakub Kicinski wrote:
> On Wed, 3 Jul 2024 14:27:58 +0200 Sebastian Andrzej Siewior wrote:
> > During the introduction of struct bpf_net_context handling for
> > XDP-redirect, the tun driver has been missed.
> >
> > Set the bpf_net_context before invoking BPF XDP program within the TUN
> > driver.
>
> Sorry if I'm missing the point but I think this is insufficient.
> You've covered the NAPI-like entry point to the Rx stack in your
> initial work, but there's also netif_receive_skb() which drivers
> may call outside of NAPI, simply disabling BH before the call.

I've seen some crashes in 6.11-rc7 that seems related to 401cb7dae8130
("net: Reference bpf_redirect_info via task_struct on PREEMPT_RT.").

Basically bpf_net_context is NULL, and it is being dereferenced by
bpf_net_ctx->ri.kern_flags (offset 0x38) in the following code.

static inline struct bpf_redirect_info *bpf_net_ctx_get_ri(void)
{
struct bpf_net_context *bpf_net_ctx = bpf_net_ctx_get();
if (!(bpf_net_ctx->ri.kern_flags & BPF_RI_F_RI_INIT)) {

That said, it means that bpf_net_ctx_get() is returning NULL.

This stack is coming from the bpf function bpf_redirect()
BPF_CALL_2(bpf_redirect, u32, ifindex, u64, flags)
{
struct bpf_redirect_info *ri = bpf_net_ctx_get_ri();

Since I don't think there is XDP involved, I wondering if we need some
preotection before calling bpf_redirect()

There is the full stack, against bc83b4d1f0869 ("Merge tag
'bcachefs-2024-09-09' of git://evilpiepirate.org/bcachefs")

[ 138.278753] BUG: kernel NULL pointer dereference, address: 0000000000000038
[ 138.292684] #PF: supervisor read access in kernel mode
[ 138.302954] #PF: error_code(0x0000) - not-present page
[ 138.313224] PGD 8fc4e6067 P4D 8fc4e6067 PUD 8fc4e5067 PMD 0
[ 138.324539] Oops: Oops: 0000 [#1] SMP
[ 138.357085] Tainted: [S]=CPU_OUT_OF_SPEC, [E]=UNSIGNED_MODULE
[ 138.368574] Hardware name: Quanta Twin Lakes MP/Twin Lakes Passive MP, BIOS F09_3A23 12/08/2020
[ 138.385971] RIP: 0010:bpf_redirect (./include/linux/filter.h:788 net/core/filter.c:2531 net/core/filter.c:2529)
[ 138.394509] Code: e9 79 ff ff ff 0f 0b cc cc cc cc cc cc cc cc cc cc cc cc cc cc 0f 1f 44 00 00 65 48 8b 04 25 00 2f 03 00 48 8b 80 20 0c 00 00 <8b> 48 38 f6 c1 02 75 2c c7 40 20 00 00 00 00 48 c7 40 18 00 00 00
All code
========
0: e9 79 ff ff ff jmp 0xffffffffffffff7e
5: 0f 0b ud2
7: cc int3
8: cc int3
9: cc int3
a: cc int3
b: cc int3
c: cc int3
d: cc int3
e: cc int3
f: cc int3
10: cc int3
11: cc int3
12: cc int3
13: cc int3
14: cc int3
15: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
1a: 65 48 8b 04 25 00 2f mov %gs:0x32f00,%rax
21: 03 00
23: 48 8b 80 20 0c 00 00 mov 0xc20(%rax),%rax
2a:* 8b 48 38 mov 0x38(%rax),%ecx <-- trapping instruction
2d: f6 c1 02 test $0x2,%cl
30: 75 2c jne 0x5e
32: c7 40 20 00 00 00 00 movl $0x0,0x20(%rax)
39: 48 rex.W
3a: c7 .byte 0xc7
3b: 40 18 00 rex sbb %al,(%rax)
...
Code starting with the faulting instruction
===========================================
0: 8b 48 38 mov 0x38(%rax),%ecx
3: f6 c1 02 test $0x2,%cl
6: 75 2c jne 0x34
8: c7 40 20 00 00 00 00 movl $0x0,0x20(%rax)
f: 48 rex.W
10: c7 .byte 0xc7
11: 40 18 00 rex sbb %al,(%rax)
...
[ 138.432073] RSP: 0018:ffffc9000f0e33d8 EFLAGS: 00010246
[ 138.442523] RAX: 0000000000000000 RBX: ffff888288d4dae0 RCX: ffff888290f6dde2
[ 138.456801] RDX: 00000000000000a8 RSI: 0000000000000000 RDI: 0000000000000002
[ 138.471080] RBP: ffffc9000f0e3450 R08: 0000000000000000 R09: 0000000000000000
[ 138.485354] R10: 0000000000000000 R11: 0000000000000005 R12: ffff88829776aa68
[ 138.499624] R13: 0000000000000002 R14: 0000000000000000 R15: 0000000000000002
[ 138.513894] FS: 00007f0a67000640(0000) GS:ffff88903f880000(0000) knlGS:0000000000000000
[ 138.530076] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 138.541562] CR2: 0000000000000038 CR3: 00000008fc4e8005 CR4: 00000000007706f0
[ 138.555830] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 138.570097] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 138.584364] PKRU: 55555554
[ 138.589769] Call Trace:
[ 138.594656] <TASK>
[ 138.598850] ? __die_body (arch/x86/kernel/dumpstack.c:421)
[ 138.605826] ? page_fault_oops (arch/x86/mm/fault.c:711)
[ 138.614017] ? exc_page_fault (./arch/x86/include/asm/irqflags.h:37 ./arch/x86/include/asm/irqflags.h:92 arch/x86/mm/fault.c:1489 arch/x86/mm/fault.c:1539)
[ 138.621859] ? asm_exc_page_fault (./arch/x86/include/asm/idtentry.h:623)
[ 138.630227] ? bpf_redirect (./include/linux/filter.h:788 net/core/filter.c:2531 net/core/filter.c:2529)
[ 138.637547] bpf_prog_61d4b6831e57702d_tw_ns_nk2phy+0x31c/0x327
[ 138.649385] ? bpf_selem_link_map (./kernel/bpf/bpf_local_storage.c:402)
[ 138.657748] netkit_xmit (./include/linux/bpf.h:1243 ./include/linux/filter.h:691 ./include/linux/filter.h:698 drivers/net/netkit.c:46 drivers/net/netkit.c:86)
[ 138.664898] dev_hard_start_xmit (./include/linux/netdevice.h:4913 ./include/linux/netdevice.h:4922 net/core/dev.c:3580 net/core/dev.c:3596)
[ 138.673263] __dev_queue_xmit (net/core/dev.h:168 net/core/dev.c:4424)
[ 138.681279] ? __dev_queue_xmit (./include/linux/bottom_half.h:? ./include/linux/rcupdate.h:890 net/core/dev.c:4348)
[ 138.689470] ip6_finish_output2 (./include/net/neighbour.h:? net/ipv6/ip6_output.c:141)
[ 138.697833] ip6_finish_output (net/ipv6/ip6_output.c:? net/ipv6/ip6_output.c:226)
[ 138.706021] ip6_output (./include/linux/netfilter.h:303 net/ipv6/ip6_output.c:247)
[ 138.712643] ? __rmqueue_pcplist (mm/page_alloc.c:2976)
[ 138.721350] ip6_xmit (net/ipv6/ip6_output.c:380)
[ 138.727976] ? refill_obj_stock.llvm.9389014391162377460 (mm/memcontrol.c:2912)
[ 138.740509] ? security_sk_classify_flow (security/security.c:?)
[ 138.750088] ? __sk_dst_check (net/core/sock.c:599)
[ 138.757756] inet6_csk_xmit (net/ipv6/inet6_connection_sock.c:135)
[ 138.765080] __tcp_transmit_skb (net/ipv4/tcp_output.c:1466)
[ 138.773445] ? _copy_from_iter (./arch/x86/include/asm/uaccess_64.h:110 ./arch/x86/include/asm/uaccess_64.h:118 ./arch/x86/include/asm/uaccess_64.h:125 lib/iov_iter.c:55 ./include/linux/iov_iter.h:51 ./include/linux/iov_iter.h:247 ./include/linux/iov_iter.h:271 lib/iov_iter.c:249 lib/iov_iter.c:260)
[ 138.781460] tcp_connect (net/ipv4/tcp_output.c:4032 net/ipv4/tcp_output.c:4142)
[ 138.788605] ? bpf_trampoline_6442578911+0x59/0xa3
[ 138.798183] tcp_v6_connect (net/ipv6/tcp_ipv6.c:333)
[ 138.805854] __inet_stream_connect (net/ipv4/af_inet.c:680)
[ 138.814565] ? __kmalloc_cache_noprof (./arch/x86/include/asm/jump_label.h:55 ./include/linux/memcontrol.h:1694 mm/slub.c:2158 mm/slub.c:4002 mm/slub.c:4041 mm/slub.c:4188)
[ 138.823795] tcp_sendmsg_fastopen (net/ipv4/tcp.c:1035)
[ 138.832507] tcp_sendmsg_locked (net/ipv4/tcp.c:1087)
[ 138.840870] ? lock_sock_nested (net/core/sock.c:3551)
[ 138.848883] ? __bpf_prog_exit_recur (./kernel/bpf/trampoline.c:909)
[ 138.857765] tcp_sendmsg (net/ipv4/tcp.c:1354)
[ 138.864562] ____sys_sendmsg.llvm.5426677171080474013 (net/socket.c:733 net/socket.c:745 net/socket.c:2597)
[ 138.876749] ? __import_iovec (./include/linux/err.h:61 lib/iov_iter.c:1282)
[ 138.884590] ___sys_sendmsg (net/socket.c:2651)
[ 138.892084] ? do_pte_missing (mm/memory.c:5019 mm/memory.c:5052 mm/memory.c:5191 mm/memory.c:3947)
[ 138.900274] ? __perf_sw_event (kernel/events/internal.h:228 kernel/events/core.c:10002 kernel/events/core.c:10027)
[ 138.908115] ? handle_mm_fault (mm/memory.c:? mm/memory.c:5858)
[ 138.916477] __x64_sys_sendmsg (net/socket.c:2680 net/socket.c:2689 net/socket.c:2687 net/socket.c:2687)
[ 138.924317] do_syscall_64 (arch/x86/entry/common.c:52 arch/x86/entry/common.c:83)
[ 138.931638] ? exc_page_fault (./arch/x86/include/asm/irqflags.h:37 ./arch/x86/include/asm/irqflags.h:92 arch/x86/mm/fault.c:1489 arch/x86/mm/fault.c:1539)
[ 138.939477] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
[ 138.949575] RIP: 0033:0x7f0b1e1293eb
[ 138.956732] Code: 48 89 e5 48 83 ec 20 89 55 ec 48 89 75 f0 89 7d f8 e8 99 a6 f6 ff 41 89 c0 8b 55 ec 48 8b 75 f0 8b 7d f8 b8 2e 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 35 44 89 c7 48 89 45 f8 e8 d1 a6 f6 ff 48 8b
All code
========
0: 48 89 e5 mov %rsp,%rbp
3: 48 83 ec 20 sub $0x20,%rsp
7: 89 55 ec mov %edx,-0x14(%rbp)
a: 48 89 75 f0 mov %rsi,-0x10(%rbp)
e: 89 7d f8 mov %edi,-0x8(%rbp)
11: e8 99 a6 f6 ff call 0xfffffffffff6a6af
16: 41 89 c0 mov %eax,%r8d
19: 8b 55 ec mov -0x14(%rbp),%edx
1c: 48 8b 75 f0 mov -0x10(%rbp),%rsi
20: 8b 7d f8 mov -0x8(%rbp),%edi
23: b8 2e 00 00 00 mov $0x2e,%eax
28: 0f 05 syscall
2a:* 48 3d 00 f0 ff ff cmp $0xfffffffffffff000,%rax <-- trapping instruction
30: 77 35 ja 0x67
32: 44 89 c7 mov %r8d,%edi
35: 48 89 45 f8 mov %rax,-0x8(%rbp)
39: e8 d1 a6 f6 ff call 0xfffffffffff6a70f
3e: 48 rex.W
3f: 8b .byte 0x8b
Code starting with the faulting instruction
===========================================
0: 48 3d 00 f0 ff ff cmp $0xfffffffffffff000,%rax
6: 77 35 ja 0x3d
8: 44 89 c7 mov %r8d,%edi
b: 48 89 45 f8 mov %rax,-0x8(%rbp)
f: e8 d1 a6 f6 ff call 0xfffffffffff6a6e5
14: 48 rex.W
15: 8b .byte 0x8b
[ 138.994291] RSP: 002b:00007f0a66ffc220 EFLAGS: 00000293 ORIG_RAX: 000000000000002e
[ 139.009429] RAX: ffffffffffffffda RBX: 00007f0a66ffc548 RCX: 00007f0b1e1293eb
[ 139.023697] RDX: 0000000020004040 RSI: 00007f0a66ffc370 RDI: 0000000000000172
[ 139.037965] RBP: 00007f0a66ffc240 R08: 0000000000000000 R09: 00007f0a66411228
[ 139.052234] R10: 00007f0a66ffc678 R11: 0000000000000293 R12: 00007f0a66ffc4c0
[ 139.066504] R13: 000000000000001c R14: 00007f0a66443000 R15: 0000000000000021
[ 139.080776] </TASK>
[ 139.085138] Modules linked in: sunrpc(E) bpf_preload(E) sch_fq(E) squashfs(E) tls(E) tcp_diag(E) inet_diag(E) act_gact(E) cls_bpf(E) intel_uncore_frequency(E) intel_uncore_frequency_common(E) skx_edac(E) skx_edac_common(E) nfit(E) libnvdimm(E) x86_pkg_temp_thermal(E) intel_powerclamp(E) coretemp(E) kvm_intel(E) iTCO_wdt(E) iTCO_vendor_support(E) evdev(E) xhci_pci(E) i2c_i801(E) kvm(E) acpi_cpufreq(E) i2c_smbus(E) xhci_hcd(E) wmi(E) ipmi_si(E) ipmi_devintf(E) ipmi_msghandler(E) button(E) sch_fq_codel(E) vhost_net(E) tun(E) vhost(E) vhost_iotlb(E) tap(E) mpls_gso(E) mpls_iptunnel(E) mpls_router(E) fou(E) loop(E) drm(E) backlight(E) drm_panel_orientation_quirks(E) autofs4(E) efivarfs(E)

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