xsk: Harden userspace-supplied xdp_desc validation

Overview

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

xsk: Harden userspace-supplied xdp_desc validation

Turned out certain clearly invalid values passed in xdp_desc from userspace can pass xp_{,un}aligned_validate_desc() and then lead to UBs or just invalid frames to be queued for xmit.

desc->len close to U32_MAX with a non-zero pool->tx_metadata_len can cause positive integer overflow and wraparound, the same way low enough desc->addr with a non-zero pool->tx_metadata_len can cause negative integer overflow. Both scenarios can then pass the validation successfully. This doesn't happen with valid XSk applications, but can be used to perform attacks.

Always promote desc->len to u64 first to exclude positive overflows of it. Use explicit check_{add,sub}_overflow() when validating desc->addr (which is u64 already).

bloat-o-meter reports a little growth of the code size:

add/remove: 0/0 grow/shrink: 2/1 up/down: 60/-16 (44) Function old new delta xskq_cons_peek_desc 299 330 +31 xsk_tx_peek_release_desc_batch 973 1002 +29 xsk_generic_xmit 3148 3132 -16

but hopefully this doesn't hurt the performance much.

Affected

• Linux >= 341ac980eab90ac1f6c22ee9f9da83ed9604d899 < 1463cd066f32efd56ddfd3ac4e3524200f362980
• Linux >= 341ac980eab90ac1f6c22ee9f9da83ed9604d899 < 5b5fffa7c81e55d8c8edf05ad40d811ec7047e21
• Linux >= 341ac980eab90ac1f6c22ee9f9da83ed9604d899 < 07ca98f906a403637fc5e513a872a50ef1247f3b
• Linux 6.8

Remediation

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