Subject: [RFC PATCH net-next v6 03/13] bpf: stop UDP sock accessing TCP fields in bpf callbacks

From: Jason Xing <[email-masked]>
Date: Tue, 21 Jan 2025 09:28:51 +0800

Applying the new member allow_tcp_access in the existing callbacks
where is_fullsock is set to 1 can help us stop UDP socket accessing
struct tcp_sock, or else it could be catastrophe leading to panic.

For now, those existing callbacks are used only for TCP. I believe
in the short run, we will have timestamping UDP callbacks support.

Signed-off-by: Jason Xing <[email-masked]>
---
 include/linux/filter.h | 1 +
 include/net/tcp.h      | 1 +
 net/core/filter.c      | 8 ++++----
 net/ipv4/tcp_input.c   | 2 ++
 net/ipv4/tcp_output.c  | 2 ++
 5 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index a3ea46281595..1b1333a90b4a 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -1508,6 +1508,7 @@ struct bpf_sock_ops_kern {
 	void	*skb_data_end;
 	u8	op;
 	u8	is_fullsock;
+	u8	allow_tcp_access;
 	u8	remaining_opt_len;
 	u64	temp;			/* temp and everything after is not
 					 * initialized to 0 before calling
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 5b2b04835688..293047694710 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -2649,6 +2649,7 @@ static inline int tcp_call_bpf(struct sock *sk, int op, u32 nargs, u32 *args)
 	memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp));
 	if (sk_fullsock(sk)) {
 		sock_ops.is_fullsock = 1;
+		sock_ops.allow_tcp_access = 1;
 		sock_owned_by_me(sk);
 	}
 
diff --git a/net/core/filter.c b/net/core/filter.c
index 8e2715b7ac8a..fdd305b4cfbb 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -10381,10 +10381,10 @@ static u32 sock_ops_convert_ctx_access(enum bpf_access_type type,
 		}							      \
 		*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(			      \
 						struct bpf_sock_ops_kern,     \
-						is_fullsock),		      \
+						allow_tcp_access),	      \
 				      fullsock_reg, si->src_reg,	      \
 				      offsetof(struct bpf_sock_ops_kern,      \
-					       is_fullsock));		      \
+					       allow_tcp_access));	      \
 		*insn++ = BPF_JMP_IMM(BPF_JEQ, fullsock_reg, 0, jmp);	      \
 		if (si->dst_reg == si->src_reg)				      \
 			*insn++ = BPF_LDX_MEM(BPF_DW, reg, si->src_reg,	      \
@@ -10469,10 +10469,10 @@ static u32 sock_ops_convert_ctx_access(enum bpf_access_type type,
 					       temp));			      \
 		*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(			      \
 						struct bpf_sock_ops_kern,     \
-						is_fullsock),		      \
+						allow_tcp_access),	      \
 				      reg, si->dst_reg,			      \
 				      offsetof(struct bpf_sock_ops_kern,      \
-					       is_fullsock));		      \
+					       allow_tcp_access));	      \
 		*insn++ = BPF_JMP_IMM(BPF_JEQ, reg, 0, 2);		      \
 		*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(			      \
 						struct bpf_sock_ops_kern, sk),\
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index eb82e01da911..77185479ed5e 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -169,6 +169,7 @@ static void bpf_skops_parse_hdr(struct sock *sk, struct sk_buff *skb)
 	memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp));
 	sock_ops.op = BPF_SOCK_OPS_PARSE_HDR_OPT_CB;
 	sock_ops.is_fullsock = 1;
+	sock_ops.allow_tcp_access = 1;
 	sock_ops.sk = sk;
 	bpf_skops_init_skb(&sock_ops, skb, tcp_hdrlen(skb));
 
@@ -185,6 +186,7 @@ static void bpf_skops_established(struct sock *sk, int bpf_op,
 	memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp));
 	sock_ops.op = bpf_op;
 	sock_ops.is_fullsock = 1;
+	sock_ops.allow_tcp_access = 1;
 	sock_ops.sk = sk;
 	/* sk with TCP_REPAIR_ON does not have skb in tcp_finish_connect */
 	if (skb)
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 0e5b9a654254..695749807c09 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -522,6 +522,7 @@ static void bpf_skops_hdr_opt_len(struct sock *sk, struct sk_buff *skb,
 		sock_owned_by_me(sk);
 
 		sock_ops.is_fullsock = 1;
+		sock_ops.allow_tcp_access = 1;
 		sock_ops.sk = sk;
 	}
 
@@ -567,6 +568,7 @@ static void bpf_skops_write_hdr_opt(struct sock *sk, struct sk_buff *skb,
 		sock_owned_by_me(sk);
 
 		sock_ops.is_fullsock = 1;
+		sock_ops.allow_tcp_access = 1;
 		sock_ops.sk = sk;
 	}
 
-- 
2.43.5