[PATCH v2 bpf-next 1/8] bpf: tcp: Convert deny-list for bpf_{get,set}sockopt() to allow-list.

[Kuniyuki Iwashima <kuniyu@google.com>]

Currently, four bpf_tcp_ops callbacks are not allowed to call
bpf_setsockopt() and bpf_getsockopt().

However, the deny-list is fragile, and when a new callback is
added, we might re-open a can of worms. [1][2]

Let's convert it to allow-list.

Note that it can be written as offsetof(,X) <= moff <= offsetof(,Y)
but clang can optimise to similar code anyway.

Link: https://lore.kernel.org/r/20220929070407.965581-5-martin.lau@linux.dev/ #[0]
Link: https://lore.kernel.org/bpf/20260421155804.135786-1-kafai.wan@linux.dev/ #[1]
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
 net/ipv4/bpf_tcp_ops.c | 39 ++++++++++++++++++++++++---------------
 1 file changed, 24 insertions(+), 15 deletions(-)

diff --git a/net/ipv4/bpf_tcp_ops.c b/net/ipv4/bpf_tcp_ops.c
index 681fed642999..1ada3b781bf1 100644
--- a/net/ipv4/bpf_tcp_ops.c
+++ b/net/ipv4/bpf_tcp_ops.c
@@ -210,6 +210,24 @@ const struct bpf_func_proto bpf_tcp_ops_get_retval_proto = {
 	.ret_type	= RET_INTEGER,
 };
 
+static bool is_sockopt_supported(u32 moff)
+{
+	switch (moff) {
+	case offsetof(struct bpf_tcp_ops, active_established):
+	case offsetof(struct bpf_tcp_ops, passive_established):
+	case offsetof(struct bpf_tcp_ops, rto):
+	case offsetof(struct bpf_tcp_ops, rtt):
+	case offsetof(struct bpf_tcp_ops, set_state):
+	case offsetof(struct bpf_tcp_ops, retrans):
+	case offsetof(struct bpf_tcp_ops, connect):
+	case offsetof(struct bpf_tcp_ops, listen):
+	case offsetof(struct bpf_tcp_ops, parse_hdr):
+		return true;
+	}
+
+	return false;
+}
+
 static const struct bpf_func_proto *
 get_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
@@ -221,22 +239,13 @@ get_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 	case BPF_FUNC_sk_storage_delete:
 		return &bpf_sk_storage_delete_proto;
 	case BPF_FUNC_setsockopt:
-		/* The sk may be an unlocked listener (synack path) or NULL
-		 * fullsock; disable for members that can run unlocked.
-		 */
-		if (moff == offsetof(struct bpf_tcp_ops, rwnd_init) ||
-		    moff == offsetof(struct bpf_tcp_ops, timeout_init) ||
-		    moff == offsetof(struct bpf_tcp_ops, hdr_opt_len) ||
-		    moff == offsetof(struct bpf_tcp_ops, write_hdr_opt))
-			return NULL;
-		return &bpf_sk_setsockopt_proto;
+		if (is_sockopt_supported(moff))
+			return &bpf_sk_setsockopt_proto;
+		return NULL;
 	case BPF_FUNC_getsockopt:
-		if (moff == offsetof(struct bpf_tcp_ops, rwnd_init) ||
-		    moff == offsetof(struct bpf_tcp_ops, timeout_init) ||
-		    moff == offsetof(struct bpf_tcp_ops, hdr_opt_len) ||
-		    moff == offsetof(struct bpf_tcp_ops, write_hdr_opt))
-			return NULL;
-		return &bpf_sk_getsockopt_proto;
+		if (is_sockopt_supported(moff))
+			return &bpf_sk_getsockopt_proto;
+		return NULL;
 	case BPF_FUNC_get_retval:
 		if (moff == offsetof(struct bpf_tcp_ops, timeout_init) ||
 		    moff == offsetof(struct bpf_tcp_ops, rwnd_init))
-- 
2.56.0.rc1.315.gc6ed9934b7-goog