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Commit 1cedee13 authored by Andrey Ignatov's avatar Andrey Ignatov Committed by Daniel Borkmann
Browse files

bpf: Hooks for sys_sendmsg 



In addition to already existing BPF hooks for sys_bind and sys_connect,
the patch provides new hooks for sys_sendmsg.

It leverages existing BPF program type `BPF_PROG_TYPE_CGROUP_SOCK_ADDR`
that provides access to socket itlself (properties like family, type,
protocol) and user-passed `struct sockaddr *` so that BPF program can
override destination IP and port for system calls such as sendto(2) or
sendmsg(2) and/or assign source IP to the socket.

The hooks are implemented as two new attach types:
`BPF_CGROUP_UDP4_SENDMSG` and `BPF_CGROUP_UDP6_SENDMSG` for UDPv4 and
UDPv6 correspondingly.

UDPv4 and UDPv6 separate attach types for same reason as sys_bind and
sys_connect hooks, i.e. to prevent reading from / writing to e.g.
user_ip6 fields when user passes sockaddr_in since it'd be out-of-bound.

The difference with already existing hooks is sys_sendmsg are
implemented only for unconnected UDP.

For TCP it doesn't make sense to change user-provided `struct sockaddr *`
at sendto(2)/sendmsg(2) time since socket either was already connected
and has source/destination set or wasn't connected and call to
sendto(2)/sendmsg(2) would lead to ENOTCONN anyway.

Connected UDP is already handled by sys_connect hooks that can override
source/destination at connect time and use fast-path later, i.e. these
hooks don't affect UDP fast-path.

Rewriting source IP is implemented differently than that in sys_connect
hooks. When sys_sendmsg is used with unconnected UDP it doesn't work to
just bind socket to desired local IP address since source IP can be set
on per-packet basis by using ancillary data (cmsg(3)). So no matter if
socket is bound or not, source IP has to be rewritten on every call to
sys_sendmsg.

To do so two new fields are added to UAPI `struct bpf_sock_addr`;
* `msg_src_ip4` to set source IPv4 for UDPv4;
* `msg_src_ip6` to set source IPv6 for UDPv6.

Signed-off-by: default avatarAndrey Ignatov <rdna@fb.com>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarMartin KaFai Lau <kafai@fb.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parent 13193b0f

include/linux/bpf-cgroup.h

+17 −6
Original line number Diff line number Diff line
@@ -66,7 +66,8 @@ int __cgroup_bpf_run_filter_sk(struct sock *sk, 


int __cgroup_bpf_run_filter_sock_addr(struct sock *sk,

				      struct sockaddr *uaddr,

				      enum bpf_attach_type type);

				      enum bpf_attach_type type,

				      void *t_ctx);



int __cgroup_bpf_run_filter_sock_ops(struct sock *sk,

				     struct bpf_sock_ops_kern *sock_ops,
@@ -120,16 +121,18 @@ int __cgroup_bpf_check_dev_permission(short dev_type, u32 major, u32 minor, 
({									       \

	int __ret = 0;							       \

	if (cgroup_bpf_enabled)						       \

		__ret = __cgroup_bpf_run_filter_sock_addr(sk, uaddr, type);    \

		__ret = __cgroup_bpf_run_filter_sock_addr(sk, uaddr, type,     \

							  NULL);	       \

	__ret;								       \

})



#define BPF_CGROUP_RUN_SA_PROG_LOCK(sk, uaddr, type)			       \

#define BPF_CGROUP_RUN_SA_PROG_LOCK(sk, uaddr, type, t_ctx)		       \

({									       \

	int __ret = 0;							       \

	if (cgroup_bpf_enabled)	{					       \

		lock_sock(sk);						       \

		__ret = __cgroup_bpf_run_filter_sock_addr(sk, uaddr, type);    \

		__ret = __cgroup_bpf_run_filter_sock_addr(sk, uaddr, type,     \

							  t_ctx);	       \

		release_sock(sk);					       \

	}								       \

	__ret;								       \
@@ -151,10 +154,16 @@ int __cgroup_bpf_check_dev_permission(short dev_type, u32 major, u32 minor, 
	BPF_CGROUP_RUN_SA_PROG(sk, uaddr, BPF_CGROUP_INET6_CONNECT)



#define BPF_CGROUP_RUN_PROG_INET4_CONNECT_LOCK(sk, uaddr)		       \

	BPF_CGROUP_RUN_SA_PROG_LOCK(sk, uaddr, BPF_CGROUP_INET4_CONNECT)

	BPF_CGROUP_RUN_SA_PROG_LOCK(sk, uaddr, BPF_CGROUP_INET4_CONNECT, NULL)



#define BPF_CGROUP_RUN_PROG_INET6_CONNECT_LOCK(sk, uaddr)		       \

	BPF_CGROUP_RUN_SA_PROG_LOCK(sk, uaddr, BPF_CGROUP_INET6_CONNECT)

	BPF_CGROUP_RUN_SA_PROG_LOCK(sk, uaddr, BPF_CGROUP_INET6_CONNECT, NULL)



#define BPF_CGROUP_RUN_PROG_UDP4_SENDMSG_LOCK(sk, uaddr, t_ctx)		       \

	BPF_CGROUP_RUN_SA_PROG_LOCK(sk, uaddr, BPF_CGROUP_UDP4_SENDMSG, t_ctx)



#define BPF_CGROUP_RUN_PROG_UDP6_SENDMSG_LOCK(sk, uaddr, t_ctx)		       \

	BPF_CGROUP_RUN_SA_PROG_LOCK(sk, uaddr, BPF_CGROUP_UDP6_SENDMSG, t_ctx)



#define BPF_CGROUP_RUN_PROG_SOCK_OPS(sock_ops)				       \

({									       \
@@ -198,6 +207,8 @@ static inline int cgroup_bpf_inherit(struct cgroup *cgrp) { return 0; } 
#define BPF_CGROUP_RUN_PROG_INET4_CONNECT_LOCK(sk, uaddr) ({ 0; })

#define BPF_CGROUP_RUN_PROG_INET6_CONNECT(sk, uaddr) ({ 0; })

#define BPF_CGROUP_RUN_PROG_INET6_CONNECT_LOCK(sk, uaddr) ({ 0; })

#define BPF_CGROUP_RUN_PROG_UDP4_SENDMSG_LOCK(sk, uaddr, t_ctx) ({ 0; })

#define BPF_CGROUP_RUN_PROG_UDP6_SENDMSG_LOCK(sk, uaddr, t_ctx) ({ 0; })

#define BPF_CGROUP_RUN_PROG_SOCK_OPS(sock_ops) ({ 0; })

#define BPF_CGROUP_RUN_PROG_DEVICE_CGROUP(type,major,minor,access) ({ 0; })

include/linux/filter.h

+1 −0
Original line number Diff line number Diff line
@@ -1010,6 +1010,7 @@ struct bpf_sock_addr_kern { 
	 * only two (src and dst) are available at convert_ctx_access time

	 */

	u64 tmp_reg;

	void *t_ctx;	/* Attach type specific context. */

};



struct bpf_sock_ops_kern {

include/uapi/linux/bpf.h

+8 −0
Original line number Diff line number Diff line
@@ -160,6 +160,8 @@ enum bpf_attach_type { 
	BPF_CGROUP_INET6_CONNECT,

	BPF_CGROUP_INET4_POST_BIND,

	BPF_CGROUP_INET6_POST_BIND,

	BPF_CGROUP_UDP4_SENDMSG,

	BPF_CGROUP_UDP6_SENDMSG,

	__MAX_BPF_ATTACH_TYPE

};
@@ -2363,6 +2365,12 @@ struct bpf_sock_addr { 
	__u32 family;		/* Allows 4-byte read, but no write */

	__u32 type;		/* Allows 4-byte read, but no write */

	__u32 protocol;		/* Allows 4-byte read, but no write */

	__u32 msg_src_ip4;	/* Allows 1,2,4-byte read an 4-byte write.

				 * Stored in network byte order.

				 */

	__u32 msg_src_ip6[4];	/* Allows 1,2,4-byte read an 4-byte write.

				 * Stored in network byte order.

				 */

};



/* User bpf_sock_ops struct to access socket values and specify request ops

kernel/bpf/cgroup.c

+10 −1
Original line number Diff line number Diff line
@@ -500,6 +500,7 @@ EXPORT_SYMBOL(__cgroup_bpf_run_filter_sk); 
 * @sk: sock struct that will use sockaddr

 * @uaddr: sockaddr struct provided by user

 * @type: The type of program to be exectuted

 * @t_ctx: Pointer to attach type specific context

 *

 * socket is expected to be of type INET or INET6.

 *
@@ -508,12 +509,15 @@ EXPORT_SYMBOL(__cgroup_bpf_run_filter_sk); 
 */

int __cgroup_bpf_run_filter_sock_addr(struct sock *sk,

				      struct sockaddr *uaddr,

				      enum bpf_attach_type type)

				      enum bpf_attach_type type,

				      void *t_ctx)

{

	struct bpf_sock_addr_kern ctx = {

		.sk = sk,

		.uaddr = uaddr,

		.t_ctx = t_ctx,

	};

	struct sockaddr_storage unspec;

	struct cgroup *cgrp;

	int ret;
@@ -523,6 +527,11 @@ int __cgroup_bpf_run_filter_sock_addr(struct sock *sk, 
	if (sk->sk_family != AF_INET && sk->sk_family != AF_INET6)

		return 0;



	if (!ctx.uaddr) {

		memset(&unspec, 0, sizeof(unspec));

		ctx.uaddr = (struct sockaddr *)&unspec;

	}



	cgrp = sock_cgroup_ptr(&sk->sk_cgrp_data);

	ret = BPF_PROG_RUN_ARRAY(cgrp->bpf.effective[type], &ctx, BPF_PROG_RUN);

kernel/bpf/syscall.c

+8 −0
Original line number Diff line number Diff line
@@ -1249,6 +1249,8 @@ bpf_prog_load_check_attach_type(enum bpf_prog_type prog_type, 
		case BPF_CGROUP_INET6_BIND:

		case BPF_CGROUP_INET4_CONNECT:

		case BPF_CGROUP_INET6_CONNECT:

		case BPF_CGROUP_UDP4_SENDMSG:

		case BPF_CGROUP_UDP6_SENDMSG:

			return 0;

		default:

			return -EINVAL;
@@ -1565,6 +1567,8 @@ static int bpf_prog_attach(const union bpf_attr *attr) 
	case BPF_CGROUP_INET6_BIND:

	case BPF_CGROUP_INET4_CONNECT:

	case BPF_CGROUP_INET6_CONNECT:

	case BPF_CGROUP_UDP4_SENDMSG:

	case BPF_CGROUP_UDP6_SENDMSG:

		ptype = BPF_PROG_TYPE_CGROUP_SOCK_ADDR;

		break;

	case BPF_CGROUP_SOCK_OPS:
@@ -1635,6 +1639,8 @@ static int bpf_prog_detach(const union bpf_attr *attr) 
	case BPF_CGROUP_INET6_BIND:

	case BPF_CGROUP_INET4_CONNECT:

	case BPF_CGROUP_INET6_CONNECT:

	case BPF_CGROUP_UDP4_SENDMSG:

	case BPF_CGROUP_UDP6_SENDMSG:

		ptype = BPF_PROG_TYPE_CGROUP_SOCK_ADDR;

		break;

	case BPF_CGROUP_SOCK_OPS:
@@ -1692,6 +1698,8 @@ static int bpf_prog_query(const union bpf_attr *attr, 
	case BPF_CGROUP_INET6_POST_BIND:

	case BPF_CGROUP_INET4_CONNECT:

	case BPF_CGROUP_INET6_CONNECT:

	case BPF_CGROUP_UDP4_SENDMSG:

	case BPF_CGROUP_UDP6_SENDMSG:

	case BPF_CGROUP_SOCK_OPS:

	case BPF_CGROUP_DEVICE:

		break;