netdev - [PATCH v3 bpf-next 2/5] bpf: Move the "cdg" tcp-cc check to the common sol_tcp

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Date:   Thu, 29 Sep 2022 00:04:04 -0700
From:   Martin KaFai Lau <martin.lau@...ux.dev>
To:     ' ' <bpf@...r.kernel.org>, ' ' <netdev@...r.kernel.org>
Cc:     'Alexei Starovoitov ' <ast@...nel.org>,
        'Andrii Nakryiko ' <andrii@...nel.org>,
        'Daniel Borkmann ' <daniel@...earbox.net>,
        'David Miller ' <davem@...emloft.net>,
        'Jakub Kicinski ' <kuba@...nel.org>,
        'Eric Dumazet ' <edumazet@...gle.com>,
        'Paolo Abeni ' <pabeni@...hat.com>, ' ' <kernel-team@...com>
Subject: [PATCH v3 bpf-next 2/5] bpf: Move the "cdg" tcp-cc check to the common sol_tcp_sockopt()

From: Martin KaFai Lau <martin.lau@...nel.org>

The check on the tcp-cc, "cdg", is done in the bpf_sk_setsockopt which is
used by the bpf_tcp_ca, bpf_lsm, cg_sockopt, and tcp_iter hooks.
However, it is not done for cg sock_ddr, cg sockops, and some of
the bpf_lsm_cgroup hooks.

The tcp-cc "cdg" should have very limited usage.  This patch is to
move the "cdg" check to the common sol_tcp_sockopt() so that all
hooks have a consistent behavior.   The motivation to make
this check consistent now is because the latter patch will
refactor the bpf_setsockopt(TCP_CONGESTION) into another function,
so it is better to take this chance to refactor this piece
also.

Signed-off-by: Martin KaFai Lau <martin.lau@...nel.org>
---
 net/core/filter.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 2fd9449026aa..f4cea3ff994a 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -5127,6 +5127,13 @@ static int sol_tcp_sockopt(struct sock *sk, int optname,
 	case TCP_CONGESTION:
 		if (*optlen < 2)
 			return -EINVAL;
+		/* "cdg" is the only cc that alloc a ptr
+		 * in inet_csk_ca area.  The bpf-tcp-cc may
+		 * overwrite this ptr after switching to cdg.
+		 */
+		if (!getopt && *optlen >= sizeof("cdg") - 1 &&
+		    !strncmp("cdg", optval, *optlen))
+			return -ENOTSUPP;
 		break;
 	case TCP_SAVED_SYN:
 		if (*optlen < 1)
@@ -5285,12 +5292,6 @@ static int _bpf_getsockopt(struct sock *sk, int level, int optname,
 BPF_CALL_5(bpf_sk_setsockopt, struct sock *, sk, int, level,
 	   int, optname, char *, optval, int, optlen)
 {
-	if (level == SOL_TCP && optname == TCP_CONGESTION) {
-		if (optlen >= sizeof("cdg") - 1 &&
-		    !strncmp("cdg", optval, optlen))
-			return -ENOTSUPP;
-	}
-
 	return _bpf_setsockopt(sk, level, optname, optval, optlen);
 }
 
-- 
2.30.2