tcp: fix use-after-free in do_tcp_getsockopt(TCP_CONGESTION)

Overview

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

tcp: fix use-after-free in do_tcp_getsockopt(TCP_CONGESTION)

do_tcp_getsockopt() reads icsk->icsk_ca_ops->name without holding rcu_read_lock(). Since commit 0baf26b0fcd7 ("bpf: tcp: Support tcp_congestion_ops in bpf"), icsk_ca_ops can point to dynamically allocated BPF struct_ops memory that may be freed concurrently via setsockopt(TCP_CONGESTION), leading to a use-after-free.

BUG: KASAN: slab-use-after-free in _copy_to_user+0x37/0x60 Read of size 16 at addr ffff888013505260 by task exploit/149 _copy_to_user+0x37/0x60 do_tcp_getsockopt+0x158a/0x2460 (net/ipv4/tcp.c:4585) tcp_getsockopt+0x91/0xf0 __sys_getsockopt+0xf7/0x170

Fix this by holding rcu_read_lock() around the ca_ops->name access, using READ_ONCE() to load icsk_ca_ops, and copying the name to a stack buffer before releasing the lock. Also annotate the relevant icsk_ca_ops stores with WRITE_ONCE() to fix the accompanying KCSAN data-race issue.

Affected

• Linux >= 0baf26b0fcd74bbfcef53c5d5e8bad2b99c8d0d2 < c1804ef016392dd91267d2207ee43b1de34302ca
• Linux >= 0baf26b0fcd74bbfcef53c5d5e8bad2b99c8d0d2 < a8e45471afa230c1431c26c8e99ec24377e3b514
• Linux >= 0baf26b0fcd74bbfcef53c5d5e8bad2b99c8d0d2 < 5271b79b7ad68dcb222e893773f92bdabf7750f3
• Linux 5.6

Remediation

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