eth: bnxt: fix kernel panic in the bnxt_get_queue_stats{rx | tx}

In the Linux kernel, the following vulnerability has been resolved:

eth: bnxt: fix kernel panic in the bnxt_get_queue_stats{rx | tx}

When qstats-get operation is executed, callbacks of netdev_stats_ops

are called. The bnxt_get_queue_stats{rx | tx} collect per-queue stats

from sw_stats in the rings.

But {rx | tx | cp}_ring are allocated when the interface is up.

So, these rings are not allocated when the interface is down.

The qstats-get is allowed even if the interface is down. However,

the bnxt_get_queue_stats{rx | tx}() accesses cp_ring and tx_ring

without null check.

So, it needs to avoid accessing rings if the interface is down.

Reproducer:

ip link set $interface down

./cli.py --spec netdev.yaml --dump qstats-get

OR

ip link set $interface down

python ./stats.py

Splat looks like:

BUG: kernel NULL pointer dereference, address: 0000000000000000

#PF: supervisor read access in kernel mode

#PF: error_code(0x0000) - not-present page

PGD 1680fa067 P4D 1680fa067 PUD 16be3b067 PMD 0

Oops: Oops: 0000 [#1] PREEMPT SMP NOPTI

CPU: 0 UID: 0 PID: 1495 Comm: python3 Not tainted 6.14.0-rc4+ #32 5cd0f999d5a15c574ac72b3e4b907341

Hardware name: ASUS System Product Name/PRIME Z690-P D4, BIOS 0603 11/01/2021

RIP: 0010:bnxt_get_queue_stats_rx+0xf/0x70 [bnxt_en]

Code: c6 87 b5 18 00 00 02 eb a2 66 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1f 44 01

RSP: 0018:ffffabef43cdb7e0 EFLAGS: 00010282

RAX: 0000000000000000 RBX: ffffffffc04c8710 RCX: 0000000000000000

RDX: ffffabef43cdb858 RSI: 0000000000000000 RDI: ffff8d504e850000

RBP: ffff8d506c9f9c00 R08: 0000000000000004 R09: ffff8d506bcd901c

R10: 0000000000000015 R11: ffff8d506bcd9000 R12: 0000000000000000

R13: ffffabef43cdb8c0 R14: ffff8d504e850000 R15: 0000000000000000

FS: 00007f2c5462b080(0000) GS:ffff8d575f600000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 0000000000000000 CR3: 0000000167fd0000 CR4: 00000000007506f0

PKRU: 55555554

Call Trace:

<TASK>

? __die+0x20/0x70

? page_fault_oops+0x15a/0x460

? sched_balance_find_src_group+0x58d/0xd10

? exc_page_fault+0x6e/0x180

? asm_exc_page_fault+0x22/0x30

? bnxt_get_queue_stats_rx+0xf/0x70 [bnxt_en cdd546fd48563c280cfd30e9647efa420db07bf1]

netdev_nl_stats_by_netdev+0x2b1/0x4e0

? xas_load+0x9/0xb0

? xas_find+0x183/0x1d0

? xa_find+0x8b/0xe0

netdev_nl_qstats_get_dumpit+0xbf/0x1e0

genl_dumpit+0x31/0x90

netlink_dump+0x1a8/0x360