net/mlx5e: Fix publication race for priv->channel_stats[]

Overview

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

net/mlx5e: Fix publication race for priv->channel_stats[]

mlx5e_channel_stats_alloc() publishes a new entry to priv->channel_stats[] and then increments priv->stats_nch as a publication token, but neither store carries any memory barrier:

priv->channel_stats[ix] = kvzalloc_node(...);
if (!priv->channel_stats[ix])
	return -ENOMEM;
priv->stats_nch++;

Concurrent readers compute the loop bound from priv->stats_nch and then dereference priv->channel_stats[i] using plain accesses, e.g.

for (i = 0; i < priv->stats_nch; i++) {
	struct mlx5e_channel_stats *cs = priv->channel_stats[i];
	... cs->rq.packets ...
}

On weakly-ordered architectures (ARM, PowerPC, RISC-V) the writes to channel_stats[ix] and stats_nch may become visible to other CPUs out of program order. A reader can observe stats_nch == N while still seeing channel_stats[N-1] == NULL, leading to a NULL pointer dereference in the channel_stats loop.

This has been observed in production on BlueField-3 DPUs (arm64), where ovs-vswitchd queries netdev statistics over netlink during NIC bringup, racing mlx5e_open_channel() -> mlx5e_channel_stats_alloc() on another CPU:

Unable to handle kernel NULL pointer dereference at virtual address 0x840 Hardware name: BlueField-3 DPU pc : mlx5e_fold_sw_stats64+0x30/0x180 [mlx5_core] Call trace: mlx5e_fold_sw_stats64+0x30/0x180 [mlx5_core] dev_get_stats+0x50/0xc0 ovs_vport_get_stats+0x38/0xac [openvswitch] ovs_vport_cmd_fill_info+0x194/0x290 [openvswitch] ovs_vport_cmd_get+0xbc/0x10c [openvswitch] genl_family_rcv_msg_doit+0xd0/0x160 genl_rcv_msg+0xec/0x1f0 netlink_rcv_skb+0x64/0x130 genl_rcv+0x40/0x60 netlink_unicast+0x2fc/0x370 netlink_sendmsg+0x1dc/0x454 ... __arm64_sys_sendmsg+0x2c/0x40

Add mlx5e_stats_nch_write() and mlx5e_stats_nch_read() helpers in en.h that wrap the smp_store_release()/smp_load_acquire() pair on stats_nch. The release/acquire pair establishes the contract:

stats_nch == N => channel_stats[0..N-1] are visible and non-NULL.

Publish the stats_nch increment via mlx5e_stats_nch_write() in the writer (mlx5e_channel_stats_alloc()), and read stats_nch via mlx5e_stats_nch_read() in all readers: mlx5e RX/TX queue stats, mlx5e_get_base_stats(), ethtool channels stats, IPoIB stats, the sw_stats fold and the HV VHCA stats agent.

Affected

• Linux >= fa691d0c9c0812b9045f3a9420862e47b3b92518 < 268869794170af37727816ad02051808adb9c9c3
• Linux >= fa691d0c9c0812b9045f3a9420862e47b3b92518 < acd34d24342a28794e706ce8191ca6c3114a38ae
• Linux >= fa691d0c9c0812b9045f3a9420862e47b3b92518 < 5c7e3755abf663f033de24f917b77685e9543045
• Linux >= fa691d0c9c0812b9045f3a9420862e47b3b92518 < 815515ec68f527ca755cb1e2c1ff9148f6b3ea56
• Linux >= fa691d0c9c0812b9045f3a9420862e47b3b92518 < 5a799714e8ca0bce9ea40694f49914cf1adbbaa9
• Linux 5.17

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.