| Message ID | 20250317092257.68760-3-jiayuan.chen@linux.dev (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | bpf: Fix use-after-free of sockmap | expand |
On Mon, Mar 17, 2025 at 05:22:55PM +0800, Jiayuan Chen wrote: > There are potential concurrency issues, as shown below. > ''' > CPU0 CPU1 > sk_psock_verdict_data_ready: > socket *sock = sk->sk_socket > if (!sock) return > close(fd): > ... > ops->release() > if (!sock->ops) return > sock->ops = NULL > rcu_call(sock) > free(sock) > READ_ONCE(sock->ops) > ^ > use 'sock' after free > ''' > > RCU is not applicable to Unix sockets read path, because the Unix socket > implementation itself assumes it's always in process context and heavily > uses mutex_lock, so, we can't call read_skb within rcu lock. Hm, I guess the RCU work in sk_psock_drop() does not work for Unix domain sockets either? Thanks.
March 20, 2025 at 08:34, "Cong Wang" <xiyou.wangcong@gmail.com> wrote: > > On Mon, Mar 17, 2025 at 05:22:55PM +0800, Jiayuan Chen wrote: > > > > > There are potential concurrency issues, as shown below. > > > > ''' > > > > CPU0 CPU1 > > > > sk_psock_verdict_data_ready: > > > > socket *sock = sk->sk_socket > > > > if (!sock) return > > > > close(fd): > > > > ... > > > > ops->release() > > > > if (!sock->ops) return > > > > sock->ops = NULL > > > > rcu_call(sock) > > > > free(sock) > > > > READ_ONCE(sock->ops) > > > > ^ > > > > use 'sock' after free > > > > ''' > > > > > > > > RCU is not applicable to Unix sockets read path, because the Unix socket > > > > implementation itself assumes it's always in process context and heavily > > > > uses mutex_lock, so, we can't call read_skb within rcu lock. > > > > Hm, I guess the RCU work in sk_psock_drop() does not work for Unix > > domain sockets either? > > Thanks. > Although the Unix domain socket framework does not use RCU locks, the entire sockmap process protects access to psock via RCU: ''' rcu_read_lock(); psock = sk_psock(sk_other); if (psock) { ... } rcu_read_unlock(); // `sk_psock_drop` will not execute until the unlock ''' Therefore, I believe there are no issues with the psock operations here. Thanks~
diff --git a/net/core/skmsg.c b/net/core/skmsg.c index 6101c1bb279a..5e913b62929e 100644 --- a/net/core/skmsg.c +++ b/net/core/skmsg.c @@ -1231,17 +1231,24 @@ static int sk_psock_verdict_recv(struct sock *sk, struct sk_buff *skb) static void sk_psock_verdict_data_ready(struct sock *sk) { - struct socket *sock = sk->sk_socket; + struct socket *sock; const struct proto_ops *ops; int copied; trace_sk_data_ready(sk); - if (unlikely(!sock)) + rcu_read_lock(); + sock = sk->sk_socket; + if (unlikely(!sock)) { + rcu_read_unlock(); return; + } ops = READ_ONCE(sock->ops); - if (!ops || !ops->read_skb) + if (!ops || !ops->read_skb) { + rcu_read_unlock(); return; + } + rcu_read_unlock(); copied = ops->read_skb(sk, sk_psock_verdict_recv); if (copied >= 0) { struct sk_psock *psock;
There are potential concurrency issues, as shown below. ''' CPU0 CPU1 sk_psock_verdict_data_ready: socket *sock = sk->sk_socket if (!sock) return close(fd): ... ops->release() if (!sock->ops) return sock->ops = NULL rcu_call(sock) free(sock) READ_ONCE(sock->ops) ^ use 'sock' after free ''' RCU is not applicable to Unix sockets read path, because the Unix socket implementation itself assumes it's always in process context and heavily uses mutex_lock, so, we can't call read_skb within rcu lock. Incrementing the psock reference count would not help either, since sock_map_close() does not wait for data_ready() to complete its execution. While we don't utilize sk_socket here, implementing read_skb at the sock layer instead of socket layer might be architecturally preferable ? However, deferring this optimization as current fix adequately addresses the immediate issue. Fixes: c63829182c37 ("af_unix: Implement ->psock_update_sk_prot()") Reported-by: syzbot+dd90a702f518e0eac072@syzkaller.appspotmail.com Closes: https://lore.kernel.org/bpf/6734c033.050a0220.2a2fcc.0015.GAE@google.com/ Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev> --- net/core/skmsg.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-)