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bpf: tcp: Stop bpf_setsockopt(TCP_CONGESTION) in init ops to recur itself

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When a bad bpf prog '.init' calls
bpf_setsockopt(TCP_CONGESTION, "itself"), it will trigger this loop:

.init => bpf_setsockopt(tcp_cc) => .init => bpf_setsockopt(tcp_cc) ...
... => .init => bpf_setsockopt(tcp_cc).

It was prevented by the prog->active counter before but the prog->active
detection cannot be used in struct_ops as explained in the earlier
patch of the set.

In this patch, the second bpf_setsockopt(tcp_cc) is not allowed
in order to break the loop.  This is done by using a bit of
an existing 1 byte hole in tcp_sock to check if there is
on-going bpf_setsockopt(TCP_CONGESTION) in this tcp_sock.

Note that this essentially limits only the first '.init' can
call bpf_setsockopt(TCP_CONGESTION) to pick a fallback cc (eg. peer
does not support ECN) and the second '.init' cannot fallback to
another cc.  This applies even the second
bpf_setsockopt(TCP_CONGESTION) will not cause a loop.

Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20220929070407.965581-5-martin.lau@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Martin KaFai Lau 2022-09-29 00:04:06 -07:00 committed by Alexei Starovoitov
parent 1e7d217faa
commit 061ff04071
3 changed files with 34 additions and 1 deletions
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6
include/linux/tcp.h
View File

@ -388,6 +388,12 @@ struct tcp_sock {
u8 bpf_sock_ops_cb_flags; /* Control calling BPF programs
* values defined in uapi/linux/tcp.h
*/
u8 bpf_chg_cc_inprogress:1; /* In the middle of
* bpf_setsockopt(TCP_CONGESTION),
* it is to avoid the bpf_tcp_cc->init()
* to recur itself by calling
* bpf_setsockopt(TCP_CONGESTION, "itself").
*/
#define BPF_SOCK_OPS_TEST_FLAG(TP, ARG) (TP->bpf_sock_ops_cb_flags & ARG)
#else
#define BPF_SOCK_OPS_TEST_FLAG(TP, ARG) 0

28
net/core/filter.c
View File

@ -5105,6 +5105,9 @@ static int bpf_sol_tcp_setsockopt(struct sock *sk, int optname,
static int sol_tcp_sockopt_congestion(struct sock *sk, char *optval,
int *optlen, bool getopt)
{
struct tcp_sock *tp;
int ret;
if (*optlen < 2)
return -EINVAL;
@ -5125,8 +5128,31 @@ static int sol_tcp_sockopt_congestion(struct sock *sk, char *optval,
if (*optlen >= sizeof("cdg") - 1 && !strncmp("cdg", optval, *optlen))
return -ENOTSUPP;
return do_tcp_setsockopt(sk, SOL_TCP, TCP_CONGESTION,
/* It stops this looping
*
* .init => bpf_setsockopt(tcp_cc) => .init =>
* bpf_setsockopt(tcp_cc)" => .init => ....
*
* The second bpf_setsockopt(tcp_cc) is not allowed
* in order to break the loop when both .init
* are the same bpf prog.
*
* This applies even the second bpf_setsockopt(tcp_cc)
* does not cause a loop. This limits only the first
* '.init' can call bpf_setsockopt(TCP_CONGESTION) to
* pick a fallback cc (eg. peer does not support ECN)
* and the second '.init' cannot fallback to
* another.
*/
tp = tcp_sk(sk);
if (tp->bpf_chg_cc_inprogress)
return -EBUSY;
tp->bpf_chg_cc_inprogress = 1;
ret = do_tcp_setsockopt(sk, SOL_TCP, TCP_CONGESTION,
KERNEL_SOCKPTR(optval), *optlen);
tp->bpf_chg_cc_inprogress = 0;
return ret;
}
static int sol_tcp_sockopt(struct sock *sk, int optname,

1
net/ipv4/tcp_minisocks.c
View File

@ -541,6 +541,7 @@ struct sock *tcp_create_openreq_child(const struct sock *sk,
newtp->fastopen_req = NULL;
RCU_INIT_POINTER(newtp->fastopen_rsk, NULL);
newtp->bpf_chg_cc_inprogress = 0;
tcp_bpf_clone(sk, newsk);
__TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS);