CVE-2022-48744 Information

Description

In the Linux kernel the following vulnerability has been resolved:

net/mlx5e: Avoid field-overflowing memcpy()

In preparation for FORTIFY_SOURCE performing compile-time and run-time field bounds checking for memcpy() memmove() and memset() avoid intentionally writing across neighboring fields.

Use flexible arrays instead of zero-element arrays (which look like they are always overflowing) and split the cross-field memcpy() into two halves that can be appropriately bounds-checked by the compiler.

We were doing:

define ETH_HLEN  14
define VLAN_HLEN  4
...
define MLX5E_XDP_MIN_INLINE (ETH_HLEN + VLAN_HLEN)
...
    struct mlx5e_tx_wqe      wqe  = mlx5_wq_cyc_get_wqe(wq pi);
...
    struct mlx5_wqe_eth_seg  eseg = &wqe->eth;
    struct mlx5_wqe_data_seg dseg = wqe->data;
...
memcpy(eseg->inline_hdr.start xdptxd->data MLX5E_XDP_MIN_INLINE);

target is wqe->eth.inline_hdr.start (which the compiler sees as being 2 bytes in size) but copying 18 intending to write across start (really vlan_tci 2 bytes). The remaining 16 bytes get written into wqe->data[0] covering byte_count (4 bytes) lkey (4 bytes) and addr (8 bytes).

struct mlx5e_tx_wqe struct mlx5_wqe_ctrl_seg ctrl; / 0 16 / struct mlx5_wqe_eth_seg eth; / 16 16 / struct mlx5_wqe_data_seg data[]; / 32 0 /

    / size: 32 cachelines: 1 members: 3 /
    / last cacheline: 32 bytes /

;

struct mlx5_wqe_eth_seg u8 swp_outer_l4_offset; / 0 1 / u8 swp_outer_l3_offset; / 1 1 / u8 swp_inner_l4_offset; / 2 1 / u8 swp_inner_l3_offset; / 3 1 / u8 cs_flags; / 4 1 / u8 swp_flags; / 5 1 / __be16 mss; / 6 2 / __be32 flow_table_metadata; / 8 4 / union struct __be16 sz; / 12 2 / u8 start[2]; / 14 2 / inline_hdr; / 12 4 / struct __be16 type; / 12 2 / __be16 vlan_tci; / 14 2 / insert; / 12 4 / __be32 trailer; / 12 4 / ; / 12 4 /

    / size: 16 cachelines: 1 members: 9 /
    / last cacheline: 16 bytes /

;

struct mlx5_wqe_data_seg __be32 byte_count; / 0 4 / __be32 lkey; / 4 4 / __be64 addr; / 8 8 /

    / size: 16 cachelines: 1 members: 3 /
    / last cacheline: 16 bytes /

;

So split the memcpy() so the compiler can reason about the buffer sizes.

\pahole\ shows no size nor member offset changes to struct mlx5e_tx_wqe nor struct mlx5e_umr_wqe. \objdump -d\ shows no meaningful object code changes (i.e. only source line number induced differences and optimizations).

Reference

https://git.kernel.org/stable/c/8fbdf8c8b8ab82beab882175157650452c46493e https://git.kernel.org/stable/c/ad5185735f7dab342fdd0dd41044da4c9ccfef67