net: restrict SO_RESERVE_MEM to TCP sockets and cap max value

Overview

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

net: restrict SO_RESERVE_MEM to TCP sockets and cap max value

Commit 2bb2f5fb21b0 ("net: add new socket option SO_RESERVE_MEM") and commit d00c8ee31729 ("net: fix possible NULL deref in sock_reserve_memory") only checked sk_has_account(sk), which is true for both TCP and UDP sockets.

However, SO_RESERVE_MEM and sk_unused_reserved_mem() are currently only supported by TCP:

• On UDP sockets, sk->sk_forward_alloc is protected by sk->sk_receive_queue.lock, whereas sock_reserve_memory() and sock_release_reserved_memory() only acquire lock_sock(sk). Concurrent UDP packet reception/release and setsockopt(SO_RESERVE_MEM) corrupt sk_forward_alloc and memcg accounting.
• udp_rmem_release() reclaims excess sk_forward_alloc without accounting for sk_unused_reserved_mem(sk).

Restrict sock_reserve_memory() to TCP sockets (sk_is_tcp(sk)) for now. Supporting SO_RESERVE_MEM for UDP (acquiring sk_receive_queue.lock and honoring sk_unused_reserved_mem() in udp_rmem_release()) can be done in a future net-next series if needed.

In addition, reject val > SZ_1G with -EINVAL in sk_setsockopt(SO_RESERVE_MEM). Without an upper bound, values near INT_MAX cause sk_mem_pages(delta) and (pages << PAGE_SHIFT) to overflow 32-bit signed int, corrupting sk->sk_forward_alloc and sk->sk_reserved_mem. Using a page-aligned cap (SZ_1G) ensures that the page-rounded sk->sk_reserved_mem reported by getsockopt(SO_RESERVE_MEM) can always be passed back to setsockopt(SO_RESERVE_MEM).

Affected

• Linux >= 2bb2f5fb21b0486ff69b7b4a1fe03a760527d133 < 492e04f9a00f3cc88a1f6899417b10f3019a624e
• Linux >= 2bb2f5fb21b0486ff69b7b4a1fe03a760527d133 < 5069ce898148bd799395c5a464e006cbb840f188
• Linux >= 2bb2f5fb21b0486ff69b7b4a1fe03a760527d133 < a467b05b201b5c26be52ed3081992fa9c0387648
• Linux >= 2bb2f5fb21b0486ff69b7b4a1fe03a760527d133 < 37e02c42a00be692c06343e11779aadc45f45971
• Linux 5.16

Remediation

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