net/mlx5e: Fix HV VHCA stats zero-sized buffer allocation

Overview

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

net/mlx5e: Fix HV VHCA stats zero-sized buffer allocation

mlx5e_hv_vhca_stats_create() is called from mlx5e_nic_enable(), before mlx5e_open(). At that point priv->stats_nch is still zero, because it is only ever incremented in mlx5e_channel_stats_alloc(), which is reached only from mlx5e_open_channel().

mlx5e_hv_vhca_stats_buf_size() therefore returns 0, and kvzalloc(0, GFP_KERNEL) returns ZERO_SIZE_PTR ((void *)16) rather than NULL. The "if (!buf)" guard does not catch this, and mlx5e_hv_vhca_stats_create() completes "successfully" with priv->stats_agent.buf set to ZERO_SIZE_PTR.

Once channels are opened (priv->stats_nch > 0) and the hypervisor enables stats reporting, mlx5e_hv_vhca_stats_work() recomputes buf_len using the new non-zero stats_nch and calls memset(buf, 0, buf_len) on ZERO_SIZE_PTR, faulting at address 0x10.

Allocate the buffer based on priv->max_nch, which is set in mlx5e_priv_init() and is the upper bound on stats_nch:

• Add a separate helper mlx5e_hv_vhca_stats_buf_max_size() that returns sizeof(per_ring_stats) * max(max_nch, stats_nch), and use it for the kvzalloc() in mlx5e_hv_vhca_stats_create().
• Keep mlx5e_hv_vhca_stats_buf_size() (which returns based on stats_nch) for the worker's active payload size, so the wire format (block->rings = stats_nch) and the amount of data filled by mlx5e_hv_vhca_fill_stats() are unchanged.

The max(max_nch, stats_nch) guard handles the rare case where mlx5e_attach_netdev() recomputes max_nch downward across a detach/resume cycle while priv->stats_nch persists (mlx5e_detach_netdev does not call mlx5e_priv_cleanup, so stats_nch is only reset when the netdev is destroyed). Without the guard, the worker could compute buf_len from stats_nch and overrun the smaller buffer allocated based on the reduced max_nch.

Allocating a non-zero buffer also makes the kvzalloc() failure path in mlx5e_hv_vhca_stats_create() reachable for the first time: it returns early without (re)creating the agent. Clear priv->stats_agent.{agent,buf} in mlx5e_hv_vhca_stats_destroy() after freeing them, so that if a later create() bails out on this path, a subsequent teardown does not double-free the stale agent/buffer left from a previous enable/disable cycle.

This mirrors the existing mlx5e pattern of preallocating arrays of size max_nch (e.g. priv->channel_stats) and lazily populating entries up to stats_nch on demand.

Affected

• Linux >= fa691d0c9c0812b9045f3a9420862e47b3b92518 < 3b3a552cf88e10bb7bda88b29cf1fd8267043d50
• Linux >= fa691d0c9c0812b9045f3a9420862e47b3b92518 < 5b927dcec5f1087942bf123a82e64a3f66475f01
• Linux >= fa691d0c9c0812b9045f3a9420862e47b3b92518 < 22c1d5ecccf92c849bdca1556179aafc95794baf
• Linux >= fa691d0c9c0812b9045f3a9420862e47b3b92518 < 420aabb32da4381d8d7cdcaa6a77fad9eaceb0a4
• Linux >= fa691d0c9c0812b9045f3a9420862e47b3b92518 < abc4c56427f144c96b2827a4db3b90eb5b7349a2
• Linux >= fa691d0c9c0812b9045f3a9420862e47b3b92518 < 25f6b929c7e379cbea7cb8caa67b49b2d1efae17
• Linux 5.17

Remediation

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