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

Overview

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

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

do_tcp_getsockopt() reads icsk->icsk_ca_ops and dereferences the get_info function pointer without rcu_read_lock(). With BPF struct_ops congestion control, ca_ops can point to dynamically allocated memory that is freed concurrently, resulting in a use-after-free when the kernel dereferences or calls through the stale pointer.

BUG: KASAN: slab-use-after-free in do_tcp_getsockopt+0x2037/0x23e0 Read of size 8 at addr ffff888013701258 by task exploit/149 do_tcp_getsockopt+0x2037/0x23e0 (net/ipv4/tcp.c:4564) tcp_getsockopt+0x91/0xf0 __sys_getsockopt+0xf7/0x170

Fix this by wrapping the ca_ops load and get_info call within rcu_read_lock()/rcu_read_unlock(), and using READ_ONCE() to load the icsk_ca_ops pointer.

Affected

• Linux >= 0baf26b0fcd74bbfcef53c5d5e8bad2b99c8d0d2 < 86814e5370068ec2bf0caa6e6d55c3e5bfc6c324
• Linux >= 0baf26b0fcd74bbfcef53c5d5e8bad2b99c8d0d2 < 39aa489e85752f9de214edb0f85e4d578e57af29
• Linux >= 0baf26b0fcd74bbfcef53c5d5e8bad2b99c8d0d2 < 385e474086c2e7e29e2dded690be40dc273e20ee
• Linux 5.6

Remediation

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