BPF/XDP: kernel panic when removing an interface that is an xdp_redirect target

["Nelson, Shannon" <shannon.nelson@amd.com>]

While testing new code to support XDP in the ionic driver we found that 
we could panic the kernel by running a bind/unbind loop on the target 
interface of an xdp_redirect action.  Obviously this is a stress test 
that is abusing the system, but it does point to a window of opportunity 
in bq_enqueue() and bq_xmit_all().  I believe that while the validity of 
the target interface has been checked in __xdp_enqueue(), the interface 
can be unbound by the time either bq_enqueue() or bq_xmit_all() tries to 
use the interface.  There is no locking or reference taken on the 
interface to hold it in place before the target’s ndo_xdp_xmit() is called.

Below is a stack trace that our tester captured while running our test 
code on a RHEL 9.2 kernel – yes, I know, unpublished driver code on a 
non-upstream kernel.  But if you look at the current upstream code in 
kernel/bpf/devmap.c I think you can see what we ran into.

Other than telling users to not abuse the system with a bind/unbind 
loop, is there something we can do to limit the potential pain here? 
Without knowing what interfaces might be targeted by the users’ XDP 
programs, is there a step the originating driver can do to take 
precautions?  Did we simply miss a step in the driver, or is this an 
actual problem in the devmap code?

Thanks,
sln

[ 6118.862868] general protection fault, probably for non-canonical 
address 0x696867666564659a: 0000 [#1] PREEMPT SMP NOPTI
[ 6118.863026] CPU: 2 PID: 0 Comm: swapper/2 Kdump: loaded Tainted: G 
   OE  -------- --- 5.14.0-284.11.1.el9_2.x86_64 #1
[ 6118.863335] Hardware name: HPE ProLiant DL320 Gen11/ProLiant DL320 
Gen11, BIOS 1.30 03/01/1023
[ 6118.863515] RIP: 0010:bq_xmit_all+0x8a/0x160
[ 6118.863704] Code: de 4c 89 f1 44 89 ea e8 b4 fc ff ff 89 c6 85 c0 0f 
84 af 00 00 00 49 8b 86 d0 00 00 00 44 89 f9 48 89 da 4c 89 f7 89 74 24 
04 <48> 8b 80 38 02 00 00 ff d0 0f 1f 00 31 c9 8b 74 24 04 85 c0 41 89
[ 6118.864137] RSP: 0018:ff733629002d8e50 EFLAGS: 00010246
[ 6118.864366] RAX: 6968676665646362 RBX: ffa53628f9ea47e8 RCX: 
0000000000000001
[ 6118.864608] RDX: ffa53628f9ea47e8 RSI: 0000000000000010 RDI: 
ff1fa0f2a46c8000
[ 6118.864859] RBP: ffa53628f9ea47f0 R08: ffffffffc082e700 R09: 
ffffffffffffffff
[ 6118.865114] R10: 0000000000000040 R11: 0000000000000003 R12: 
0000000000000010
[ 6118.865380] R13: 0000000000000010 R14: ff1fa0f2a46c8000 R15: 
0000000000000001
[ 6118.865648] FS: 0000000000000000(0000) GS:ff1fa0f5af280000(0000) 
knlGS:0000000000000000
[ 6118.865928] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 6118.866213] CR2: 0000557586bae5e6 CR3: 000000001d410004 CR4: 
0000000000771ee0
[ 6118.866509] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 
0000000000000000
[ 6118.866811] DR3: 0000000000000000 DR6: 00000000fffe07f0 DR7: 
0000000000000400
[ 6118.867117] PKRU: 55555554
[ 6118.867423] Call Trace:
[ 6118.867731] <IRQ>
[ 6118.868040] __dev_flush+0x39/0xa0
[ 6118.868358] xdp_do_flush+0xa/0x20
[ 6118.868681] ionic_txrx_napi+0x1ba/0x1f0 [ionic]
[ 6118.869024] __napi_poll+0x27/0x170
[ 6118.869357] net_rx_action+0x233/0x2f0
[ 6118.869693] __do_softirq+0xc7/0x2ac
[ 6118.870037] __irq_exit_rcu+0xb5/0xe0
[ 6118.870383] common_interrupt+0x80/0xa0
[ 6118.870735] </IRQ>
[ 6118.871082] <TASK>
[ 6118.871431] asm_common_interrupt+0x22/0x40
[ 6118.871790] RIP: 0010:cpuidle_enter_state+0xd2/0x400
[ 6118.872162] Code: 49 89 c5 0f 1f 44 00 00 31 ff e8 f9 a9 8e ff 45 84 
ff 74 12 9c 58 f6 c4 02 0f 85 12 03 00 00 31 ff e8 72 b7 94 ff fb 45 85 
f6 <0f> 88 15 01 00 00 49 63 d6 4c 2b 2c 24 48 8d 04 52 48 8d 04 82 49
[ 6118.872962] RSP: 0018:ff7336290010fe80 EFLAGS: 00000206
[ 6118.873377] RAX: ff1fa0f5af2aabc0 RBX: 0000000000000003 RCX: 
000000000000001f
[ 6118.873804] RDX: 0000000000000000 RSI: 0000000055555555 RDI: 
0000000000000000
[ 6118.874236] RBP: ffa53628faaa4400 R08: 00000590a8a55399 R09: 
0000000000000001
[ 6118.874752] R10: 0000000000000400 R11: 0000000000000730 R12: 
ffffffffbacace60
[ 6118.875282] R13: 00000590a8a55399 R14: 0000000000000003 R15: 
0000000000000000
[ 6118.875737] cpuidle_enter+0x29/0x40
[ 6118.876198] cpuidle_idle_call+0x12c/0x1c0
[ 6118.876664] do_idle+0x7b/0xe0
[ 6118.877132] cpu_startup_entry+0x19/0x20
[ 6118.877604] start_secondary+0x116/0x140
[ 6118.878081] secondary_startup_64_no_verify+0xe5/0xeb
[ 6118.878562] </TASK>
[ 6118.879104] Modules linked in: ionic(OE) ib_core tls 8021q garp mrp 
stp llc nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet 
nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nft_chain_nat nf_nat 
nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 rfkill ip_set nf_tables 
nfnetlink vfat fat ipmi_ssif intel_rapl_msr intel_rapl_common nfit 
libnvdimm x86_pkg_temp_thermal intel_powerclamp coretemp kvm_intel 
pmt_crashlog pmt_telemetry pmt_class kvm irqbypass rapl intel_cstate 
cdc_eem intel_uncore idxd usbnet acpi_ipmi mei_me isst_if_mbox_pci 
isst_if_mmio pcspkr isst_if_common intel_vsec mii idxd_bus mei hpilo 
ipmi_si ipmi_devintf ipmi_msghandler acpi_tad acpi_power_meter xfs 
libcrc32c sd_mod t10_pi sg mgag200 i2c_algo_bit drm_shmem_helper 
drm_kms_helper ahci syscopyarea sysfillrect sysimgblt libahci 
fb_sys_fops qat_4xxx drm libata crct10dif_pclmul crc32_pclmul intel_qat 
crc32c_intel tg3 ghash_clmulni_intel crc8 hpwdt wmi dm_mirror 
dm_region_hash dm_log dm_mod fuse [last unloaded: ionic]