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

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do_tcp_getsockopt() reads icsk->icsk_ca_ops->name without holding
rcu_read_lock(). Since commit 0baf26b0fc ("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.

Fixes: 0baf26b0fc ("bpf: tcp: Support tcp_congestion_ops in bpf")
Suggested-by: Eric Dumazet <edumazet@google.com>
Reported-by: Xiang Mei (Microsoft) <xmei5@asu.edu>
Link: https://lore.kernel.org/all/20260821182449.79785-2-blbllhy@gmail.com/
Cc: AutonomousCodeSecurity@microsoft.com
Cc: stable@vger.kernel.org
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Cen Zhang (Microsoft Security FORGE Labs) <blbllhy@gmail.com>
Reviewed-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Reviewed-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/d3f97f1acbf0010898148be6e6406e4b8b4a5c84.1787870710.git.blbllhy@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Cen Zhang (Microsoft Security FORGE Labs) 2026-08-27 19:55:10 -04:00 committed by Jakub Kicinski
parent 7e1d6caa9c
commit 5271b79b7a
5 changed files with 16 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
net/ipv4/tcp.c
View File

@ -4576,16 +4576,24 @@ int do_tcp_getsockopt(struct sock *sk, int level,
val = !inet_csk_in_pingpong_mode(sk);
break;
case TCP_CONGESTION:
case TCP_CONGESTION: {
char ca_name[TCP_CA_NAME_MAX] = {};
if (copy_from_sockptr(&len, optlen, sizeof(int)))
return -EFAULT;
len = min_t(unsigned int, len, TCP_CA_NAME_MAX);
if (copy_to_sockptr(optlen, &len, sizeof(int)))
return -EFAULT;
if (copy_to_sockptr(optval, icsk->icsk_ca_ops->name, len))
rcu_read_lock();
memcpy(ca_name, READ_ONCE(icsk->icsk_ca_ops)->name,
sizeof(ca_name));
rcu_read_unlock();
if (copy_to_sockptr(optval, ca_name, len))
return -EFAULT;
return 0;
}
case TCP_ULP:
if (copy_from_sockptr(&len, optlen, sizeof(int)))
return -EFAULT;

4
net/ipv4/tcp_cong.c
View File

@ -223,7 +223,7 @@ void tcp_assign_congestion_control(struct sock *sk)
ca = rcu_dereference(net->ipv4.tcp_congestion_control);
if (unlikely(!bpf_try_module_get(ca, ca->owner)))
ca = &tcp_reno;
icsk->icsk_ca_ops = ca;
WRITE_ONCE(icsk->icsk_ca_ops, ca);
rcu_read_unlock();
memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
@ -253,7 +253,7 @@ static void tcp_reinit_congestion_control(struct sock *sk,
struct inet_connection_sock *icsk = inet_csk(sk);
tcp_cleanup_congestion_control(sk);
icsk->icsk_ca_ops = ca;
WRITE_ONCE(icsk->icsk_ca_ops, ca);
icsk->icsk_ca_setsockopt = 1;
memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));

2
net/ipv4/tcp_dctcp.c
View File

@ -111,7 +111,7 @@ __bpf_kfunc static void dctcp_init(struct sock *sk)
/* No ECN support? Fall back to Reno. Also need to clear
* ECT from sk since it is set during 3WHS for DCTCP.
*/
inet_csk(sk)->icsk_ca_ops = &dctcp_reno;
WRITE_ONCE(inet_csk(sk)->icsk_ca_ops, &dctcp_reno);
INET_ECN_dontxmit(sk);
}

2
net/ipv4/tcp_minisocks.c
View File

@ -507,7 +507,7 @@ void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst)
ca = tcp_ca_find_key(ca_key);
if (likely(ca && bpf_try_module_get(ca, ca->owner))) {
icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst);
icsk->icsk_ca_ops = ca;
WRITE_ONCE(icsk->icsk_ca_ops, ca);
ca_got_dst = true;
}
rcu_read_unlock();

2
net/ipv4/tcp_output.c
View File

@ -4092,7 +4092,7 @@ static void tcp_ca_dst_init(struct sock *sk, const struct dst_entry *dst)
if (likely(ca && bpf_try_module_get(ca, ca->owner))) {
bpf_module_put(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner);
icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst);
icsk->icsk_ca_ops = ca;
WRITE_ONCE(icsk->icsk_ca_ops, ca);
}
rcu_read_unlock();
}