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tcp: fix tcp_set_congestion_control() use from bpf hook 

Neal reported incorrect use of ns_capable() from bpf hook.

bpf_setsockopt(...TCP_CONGESTION...)
  -> tcp_set_congestion_control()
   -> ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN)
    -> ns_capable_common()
     -> current_cred()
      -> rcu_dereference_protected(current->cred, 1)

Accessing 'current' in bpf context makes no sense, since packets
are processed from softirq context.

As Neal stated : The capability check in tcp_set_congestion_control()
was written assuming a system call context, and then was reused from
a BPF call site.

The fix is to add a new parameter to tcp_set_congestion_control(),
so that the ns_capable() call is only performed under the right
context.

Fixes: 91b5b21c7c ("bpf: Add support for changing congestion control")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Lawrence Brakmo <brakmo@fb.com>
Reported-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Lawrence Brakmo <brakmo@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2019-07-18 19:28:14 -07:00 committed by David S. Miller
parent 269b7c5ff7
commit 8d650cdeda
4 changed files with 9 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
include/net/tcp.h
View File

@ -1064,7 +1064,8 @@ void tcp_get_default_congestion_control(struct net *net, char *name);
void tcp_get_available_congestion_control(char *buf, size_t len);
void tcp_get_allowed_congestion_control(char *buf, size_t len);
int tcp_set_allowed_congestion_control(char *allowed);
int tcp_set_congestion_control(struct sock *sk, const char *name, bool load, bool reinit);
int tcp_set_congestion_control(struct sock *sk, const char *name, bool load,
bool reinit, bool cap_net_admin);
u32 tcp_slow_start(struct tcp_sock *tp, u32 acked);
void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked);

2
net/core/filter.c
View File

@ -4335,7 +4335,7 @@ BPF_CALL_5(bpf_setsockopt, struct bpf_sock_ops_kern *, bpf_sock,
TCP_CA_NAME_MAX-1));
name[TCP_CA_NAME_MAX-1] = 0;
ret = tcp_set_congestion_control(sk, name, false,
reinit);
reinit, true);
} else {
struct tcp_sock *tp = tcp_sk(sk);

4
net/ipv4/tcp.c
View File

@ -2785,7 +2785,9 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
name[val] = 0;
lock_sock(sk);
err = tcp_set_congestion_control(sk, name, true, true);
err = tcp_set_congestion_control(sk, name, true, true,
ns_capable(sock_net(sk)->user_ns,
CAP_NET_ADMIN));
release_sock(sk);
return err;
}

6
net/ipv4/tcp_cong.c
View File

@ -333,7 +333,8 @@ out:
* tcp_reinit_congestion_control (if the current congestion control was
* already initialized.
*/
int tcp_set_congestion_control(struct sock *sk, const char *name, bool load, bool reinit)
int tcp_set_congestion_control(struct sock *sk, const char *name, bool load,
bool reinit, bool cap_net_admin)
{
struct inet_connection_sock *icsk = inet_csk(sk);
const struct tcp_congestion_ops *ca;
@ -369,8 +370,7 @@ int tcp_set_congestion_control(struct sock *sk, const char *name, bool load, boo
} else {
err = -EBUSY;
}
} else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) ||
ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN))) {
} else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) || cap_net_admin)) {
err = -EPERM;
} else if (!try_module_get(ca->owner)) {
err = -EBUSY;