bpf: Add bpf_sock_addr_set_sun_path() to allow writing unix sockaddr from bpf

As prep for adding unix socket support to the cgroup sockaddr hooks,
let's add a kfunc bpf_sock_addr_set_sun_path() that allows modifying a unix
sockaddr from bpf. While this is already possible for AF_INET and AF_INET6,
we'll need this kfunc when we add unix socket support since modifying the
address for those requires modifying both the address and the sockaddr
length.

Signed-off-by: Daan De Meyer <daan.j.demeyer@gmail.com>
Link: https://lore.kernel.org/r/20231011185113.140426-4-daan.j.demeyer@gmail.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 69101200c1245727b858cee25114e9625c2cbdf4..15d71d2986d3a1779ca2a99360be1edd6352c971 100644 (file)
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -7850,6 +7850,7 @@ static int bpf_prog_type_to_kfunc_hook(enum bpf_prog_type prog_type)
        case BPF_PROG_TYPE_SYSCALL:
                return BTF_KFUNC_HOOK_SYSCALL;
        case BPF_PROG_TYPE_CGROUP_SKB:
+       case BPF_PROG_TYPE_CGROUP_SOCK_ADDR:
                return BTF_KFUNC_HOOK_CGROUP_SKB;
        case BPF_PROG_TYPE_SCHED_ACT:
                return BTF_KFUNC_HOOK_SCHED_ACT;

diff --git a/net/core/filter.c b/net/core/filter.c
index 3880bf0b740df88be96fae1bca0dab63f33b7308..ff0bd9f20b9565dbe4979ba5e3b1c01731601ed5 100644 (file)
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -81,6 +81,7 @@
 #include <net/xdp.h>
 #include <net/mptcp.h>
 #include <net/netfilter/nf_conntrack_bpf.h>
+#include <linux/un.h>
 
 static const struct bpf_func_proto *
 bpf_sk_base_func_proto(enum bpf_func_id func_id);
@@ -11768,6 +11769,27 @@ __bpf_kfunc int bpf_dynptr_from_xdp(struct xdp_buff *xdp, u64 flags,
 
        return 0;
 }
+
+__bpf_kfunc int bpf_sock_addr_set_sun_path(struct bpf_sock_addr_kern *sa_kern,
+                                          const u8 *sun_path, u32 sun_path__sz)
+{
+       struct sockaddr_un *un;
+
+       if (sa_kern->sk->sk_family != AF_UNIX)
+               return -EINVAL;
+
+       /* We do not allow changing the address to unnamed or larger than the
+        * maximum allowed address size for a unix sockaddr.
+        */
+       if (sun_path__sz == 0 || sun_path__sz > UNIX_PATH_MAX)
+               return -EINVAL;
+
+       un = (struct sockaddr_un *)sa_kern->uaddr;
+       memcpy(un->sun_path, sun_path, sun_path__sz);
+       sa_kern->uaddrlen = offsetof(struct sockaddr_un, sun_path) + sun_path__sz;
+
+       return 0;
+}
 __diag_pop();
 
 int bpf_dynptr_from_skb_rdonly(struct sk_buff *skb, u64 flags,
@@ -11792,6 +11814,10 @@ BTF_SET8_START(bpf_kfunc_check_set_xdp)
 BTF_ID_FLAGS(func, bpf_dynptr_from_xdp)
 BTF_SET8_END(bpf_kfunc_check_set_xdp)
 
+BTF_SET8_START(bpf_kfunc_check_set_sock_addr)
+BTF_ID_FLAGS(func, bpf_sock_addr_set_sun_path)
+BTF_SET8_END(bpf_kfunc_check_set_sock_addr)
+
 static const struct btf_kfunc_id_set bpf_kfunc_set_skb = {
        .owner = THIS_MODULE,
        .set = &bpf_kfunc_check_set_skb,
@@ -11802,6 +11828,11 @@ static const struct btf_kfunc_id_set bpf_kfunc_set_xdp = {
        .set = &bpf_kfunc_check_set_xdp,
 };
 
+static const struct btf_kfunc_id_set bpf_kfunc_set_sock_addr = {
+       .owner = THIS_MODULE,
+       .set = &bpf_kfunc_check_set_sock_addr,
+};
+
 static int __init bpf_kfunc_init(void)
 {
        int ret;
@@ -11816,7 +11847,9 @@ static int __init bpf_kfunc_init(void)
        ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_LWT_XMIT, &bpf_kfunc_set_skb);
        ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_LWT_SEG6LOCAL, &bpf_kfunc_set_skb);
        ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_NETFILTER, &bpf_kfunc_set_skb);
-       return ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_XDP, &bpf_kfunc_set_xdp);
+       ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_XDP, &bpf_kfunc_set_xdp);
+       return ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_CGROUP_SOCK_ADDR,
+                                               &bpf_kfunc_set_sock_addr);
 }
 late_initcall(bpf_kfunc_init);