CVE-2022-48744

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 */...