[PATCH bpf-next 1/2] bpf: allow rewriting to ports under ip_unprivileged_port_start
From: Stanislav Fomichev <hidden>
Date: 2021-01-21 01:49:46
Also in:
bpf
Subsystem:
bpf [core], bpf [general] (safe dynamic programs and tools), bpf [networking] (tcx & tc bpf, sock_addr), networking [general], the rest · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
At the moment, BPF_CGROUP_INET{4,6}_BIND hooks can rewrite user_port
to the privileged ones (< ip_unprivileged_port_start), but it will
be rejected later on in the __inet_bind or __inet6_bind.
Let's export 'port_changed' event from the BPF program and bypass
ip_unprivileged_port_start range check when we've seen that
the program explicitly overrode the port. This is accomplished
by generating instructions to set ctx->port_changed along with
updating ctx->user_port.
Signed-off-by: Stanislav Fomichev <redacted>
---
include/linux/bpf-cgroup.h | 30 ++++++++++++++++++++----------
include/linux/filter.h | 1 +
include/net/inet_common.h | 3 +++
kernel/bpf/cgroup.c | 8 +++++++-
net/core/filter.c | 13 +++++++++++++
net/ipv4/af_inet.c | 9 ++++++---
net/ipv6/af_inet6.c | 6 ++++--
7 files changed, 54 insertions(+), 16 deletions(-)
diff --git a/include/linux/bpf-cgroup.h b/include/linux/bpf-cgroup.h
index 0748fd87969e..874ed865bea1 100644
--- a/include/linux/bpf-cgroup.h
+++ b/include/linux/bpf-cgroup.h@@ -125,7 +125,8 @@ 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, - void *t_ctx); + void *t_ctx, + bool *port_changed); int __cgroup_bpf_run_filter_sock_ops(struct sock *sk, struct bpf_sock_ops_kern *sock_ops,
@@ -234,7 +235,7 @@ int bpf_percpu_cgroup_storage_update(struct bpf_map *map, void *key, int __ret = 0; \ if (cgroup_bpf_enabled(type)) \ __ret = __cgroup_bpf_run_filter_sock_addr(sk, uaddr, type, \ - NULL); \ + NULL, NULL); \ __ret; \ })
@@ -244,17 +245,27 @@ int bpf_percpu_cgroup_storage_update(struct bpf_map *map, void *key, if (cgroup_bpf_enabled(type)) { \ lock_sock(sk); \ __ret = __cgroup_bpf_run_filter_sock_addr(sk, uaddr, type, \ - t_ctx); \ + t_ctx, NULL); \ release_sock(sk); \ } \ __ret; \ }) -#define BPF_CGROUP_RUN_PROG_INET4_BIND_LOCK(sk, uaddr) \ - BPF_CGROUP_RUN_SA_PROG_LOCK(sk, uaddr, BPF_CGROUP_INET4_BIND, NULL) - -#define BPF_CGROUP_RUN_PROG_INET6_BIND_LOCK(sk, uaddr) \ - BPF_CGROUP_RUN_SA_PROG_LOCK(sk, uaddr, BPF_CGROUP_INET6_BIND, NULL) +#define BPF_CGROUP_RUN_PROG_INET_BIND_LOCK(sk, uaddr, type, flags) \ +({ \ + bool port_changed = false; \ + int __ret = 0; \ + if (cgroup_bpf_enabled(type)) { \ + lock_sock(sk); \ + __ret = __cgroup_bpf_run_filter_sock_addr(sk, uaddr, type, \ + NULL, \ + &port_changed); \ + release_sock(sk); \ + if (port_changed) \ + *flags |= BIND_NO_CAP_NET_BIND_SERVICE; \ + } \ + __ret; \ +}) #define BPF_CGROUP_PRE_CONNECT_ENABLED(sk) \ ((cgroup_bpf_enabled(BPF_CGROUP_INET4_CONNECT) || \
@@ -453,8 +464,7 @@ static inline int bpf_percpu_cgroup_storage_update(struct bpf_map *map, #define BPF_CGROUP_RUN_PROG_INET_EGRESS(sk,skb) ({ 0; }) #define BPF_CGROUP_RUN_PROG_INET_SOCK(sk) ({ 0; }) #define BPF_CGROUP_RUN_PROG_INET_SOCK_RELEASE(sk) ({ 0; }) -#define BPF_CGROUP_RUN_PROG_INET4_BIND_LOCK(sk, uaddr) ({ 0; }) -#define BPF_CGROUP_RUN_PROG_INET6_BIND_LOCK(sk, uaddr) ({ 0; }) +#define BPF_CGROUP_RUN_PROG_INET_BIND_LOCK(sk, uaddr, type, flags) ({ 0; }) #define BPF_CGROUP_RUN_PROG_INET4_POST_BIND(sk) ({ 0; }) #define BPF_CGROUP_RUN_PROG_INET6_POST_BIND(sk) ({ 0; }) #define BPF_CGROUP_RUN_PROG_INET4_CONNECT(sk, uaddr) ({ 0; })
diff --git a/include/linux/filter.h b/include/linux/filter.h
index 5b3137d7b690..9bee8c057dd2 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h@@ -1258,6 +1258,7 @@ struct bpf_sock_addr_kern { */ u64 tmp_reg; void *t_ctx; /* Attach type specific context. */ + u32 port_changed; }; struct bpf_sock_ops_kern {
diff --git a/include/net/inet_common.h b/include/net/inet_common.h
index cb2818862919..9ba935c15869 100644
--- a/include/net/inet_common.h
+++ b/include/net/inet_common.h@@ -41,6 +41,9 @@ int inet_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len); #define BIND_WITH_LOCK (1 << 1) /* Called from BPF program. */ #define BIND_FROM_BPF (1 << 2) +/* Skip CAP_NET_BIND_SERVICE check. */ +#define BIND_NO_CAP_NET_BIND_SERVICE (1 << 3) + int __inet_bind(struct sock *sk, struct sockaddr *uaddr, int addr_len, u32 flags); int inet_getname(struct socket *sock, struct sockaddr *uaddr,
diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index da649f20d6b2..f5d6205f1717 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c@@ -1055,6 +1055,8 @@ EXPORT_SYMBOL(__cgroup_bpf_run_filter_sk); * @uaddr: sockaddr struct provided by user * @type: The type of program to be exectuted * @t_ctx: Pointer to attach type specific context + * @port_changed: Pointer to bool which will be set to 'true' when BPF + * program updates user_port * * socket is expected to be of type INET or INET6. *
@@ -1064,7 +1066,8 @@ 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, - void *t_ctx) + void *t_ctx, + bool *port_changed) { struct bpf_sock_addr_kern ctx = { .sk = sk,
@@ -1089,6 +1092,9 @@ int __cgroup_bpf_run_filter_sock_addr(struct sock *sk, cgrp = sock_cgroup_ptr(&sk->sk_cgrp_data); ret = BPF_PROG_RUN_ARRAY(cgrp->bpf.effective[type], &ctx, BPF_PROG_RUN); + if (port_changed) + *port_changed = ctx.port_changed; + return ret == 1 ? 0 : -EPERM; } EXPORT_SYMBOL(__cgroup_bpf_run_filter_sock_addr);
diff --git a/net/core/filter.c b/net/core/filter.c
index 9ab94e90d660..b3dd02eb9551 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c@@ -9028,6 +9028,19 @@ static u32 sock_addr_convert_ctx_access(enum bpf_access_type type, offsetof(struct sockaddr_in6, sin6_port)); BUILD_BUG_ON(sizeof_field(struct sockaddr_in, sin_port) != sizeof_field(struct sockaddr_in6, sin6_port)); + + /* Set bpf_sock_addr_kern->port_changed=1 whenever + * the port is updated from the BPF program. + */ + if (type == BPF_WRITE) { + *insn++ = BPF_ST_MEM(BPF_FIELD_SIZEOF(struct bpf_sock_addr_kern, + port_changed), + si->dst_reg, + offsetof(struct bpf_sock_addr_kern, + port_changed), + 1); + } + /* Account for sin6_port being smaller than user_port. */ port_size = min(port_size, BPF_LDST_BYTES(si)); SOCK_ADDR_LOAD_OR_STORE_NESTED_FIELD_SIZE_OFF(
diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index 6ba2930ff49b..aaa94bea19c3 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c@@ -438,6 +438,7 @@ EXPORT_SYMBOL(inet_release); int inet_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len) { struct sock *sk = sock->sk; + u32 flags = BIND_WITH_LOCK; int err; /* If the socket has its own bind function then use it. (RAW) */
@@ -450,11 +451,12 @@ int inet_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len) /* BPF prog is run before any checks are done so that if the prog * changes context in a wrong way it will be caught. */ - err = BPF_CGROUP_RUN_PROG_INET4_BIND_LOCK(sk, uaddr); + err = BPF_CGROUP_RUN_PROG_INET_BIND_LOCK(sk, uaddr, + BPF_CGROUP_INET4_BIND, &flags); if (err) return err; - return __inet_bind(sk, uaddr, addr_len, BIND_WITH_LOCK); + return __inet_bind(sk, uaddr, addr_len, flags); } EXPORT_SYMBOL(inet_bind);
@@ -499,7 +501,8 @@ int __inet_bind(struct sock *sk, struct sockaddr *uaddr, int addr_len, snum = ntohs(addr->sin_port); err = -EACCES; - if (snum && inet_port_requires_bind_service(net, snum) && + if (!(flags & BIND_NO_CAP_NET_BIND_SERVICE) && + snum && inet_port_requires_bind_service(net, snum) && !ns_capable(net->user_ns, CAP_NET_BIND_SERVICE)) goto out;
diff --git a/net/ipv6/af_inet6.c b/net/ipv6/af_inet6.c
index b9c654836b72..3e523c4f5226 100644
--- a/net/ipv6/af_inet6.c
+++ b/net/ipv6/af_inet6.c@@ -439,6 +439,7 @@ static int __inet6_bind(struct sock *sk, struct sockaddr *uaddr, int addr_len, int inet6_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len) { struct sock *sk = sock->sk; + u32 flags = BIND_WITH_LOCK; int err = 0; /* If the socket has its own bind function then use it. */
@@ -451,11 +452,12 @@ int inet6_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len) /* BPF prog is run before any checks are done so that if the prog * changes context in a wrong way it will be caught. */ - err = BPF_CGROUP_RUN_PROG_INET6_BIND_LOCK(sk, uaddr); + err = BPF_CGROUP_RUN_PROG_INET_BIND_LOCK(sk, uaddr, + BPF_CGROUP_INET6_BIND, &flags); if (err) return err; - return __inet6_bind(sk, uaddr, addr_len, BIND_WITH_LOCK); + return __inet6_bind(sk, uaddr, addr_len, flags); } EXPORT_SYMBOL(inet6_bind);
--
2.30.0.284.gd98b1dd5eaa7-goog