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 / __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).