Re: [PATCH net v2 1/2] tcp: fix use-after-free in do_tcp_getsockopt(TCP_CONGESTION)

[Eric Dumazet]

On Wed, Aug 26, 2026 at 7:14 PM Cen Zhang (Microsoft) <blbllhy@xxxxxxxxx> wrote:
>
> From: "Cen Zhang (Microsoft Security FORGE Labs)" <blbllhy@xxxxxxxxx>
>
> 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 every explicit
> icsk_ca_ops store with WRITE_ONCE() to fix the accompanying KCSAN
> data-race issue.
>
> Fixes: 0baf26b0fcd7 ("bpf: tcp: Support tcp_congestion_ops in bpf")
> Suggested-by: Eric Dumazet <edumazet@xxxxxxxxxx>
> Reported-by: Xiang Mei (Microsoft) <xmei5@xxxxxxx>
> Link: https://lore.kernel.org/all/20260821182449.79785-2-blbllhy@xxxxxxxxx/
> Cc: AutonomousCodeSecurity@xxxxxxxxxxxxx
> Cc: stable@xxxxxxxxxxxxxxx
> Assisted-by: GitHub-Copilot:claude-opus-4.6
> Signed-off-by: Cen Zhang (Microsoft Security FORGE Labs) <blbllhy@xxxxxxxxx>
> ---

Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>

Thanks.