Re: [PATCH net 2/2] tcp: fix use-after-free in do_tcp_getsockopt(TCP_CC_INFO)

On Fri, Aug 21, 2026 at 8:25 PM Cen Zhang (Microsoft) [off-list ref] wrote:

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().

Fixes: 0baf26b0fcd7 ("bpf: tcp: Support tcp_congestion_ops in bpf")
Reported-by: AutonomousCodeSecurity@microsoft.com
Reported-by: Cen Zhang (Microsoft) <redacted>
Cc: stable@vger.kernel.org
Signed-off-by: Cen Zhang (Microsoft) <redacted>
---
The unsynchronized icsk_ca_ops load also constitutes a data race.
READ_ONCE()/WRITE_ONCE() annotations are intentionally left to a
separate change; related TCP annotation work is available at:
https://lore.kernel.org/all/20260416200319.3608680-1-edumazet@google.com/ (local)

I don't understand.

This patch is incomplete. Please fix the remaining issues in a single
patch or series.

We have limited time; we don't want to revisit the same area  in one month.

pw-bot: cr