On 10/26/2016 12:30 AM, David Ahern wrote:
Add new cgroup based program type, BPF_PROG_TYPE_CGROUP_SOCK. Similar to
BPF_PROG_TYPE_CGROUP_SKB programs can be attached to a cgroup and run
any time a process in the cgroup opens an AF_INET or AF_INET6 socket.
Currently only sk_bound_dev_if is exported to userspace for modification
by a bpf program.
This allows a cgroup to be configured such that AF_INET{6} sockets opened
by processes are automatically bound to a specific device. In turn, this
enables the running of programs that do not support SO_BINDTODEVICE in a
specific VRF context / L3 domain.
Signed-off-by: David Ahern <d...@cumulusnetworks.com>
[...]
@@ -524,6 +535,10 @@ struct bpf_tunnel_key {
__u32 tunnel_label;
};
+struct bpf_sock {
+ __u32 bound_dev_if;
+};
+
/* User return codes for XDP prog type.
* A valid XDP program must return one of these defined values. All other
* return codes are reserved for future use. Unknown return codes will result
[...]
diff --git a/net/core/filter.c b/net/core/filter.c
index 4552b8c93b99..775802881b01 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2482,6 +2482,27 @@ static const struct bpf_func_proto
bpf_xdp_event_output_proto = {
.arg5_type = ARG_CONST_STACK_SIZE,
};
+BPF_CALL_3(bpf_sock_store_u32, struct sock *, sk, u32, offset, u32, val)
+{
+ u8 *ptr = (u8 *)sk;
+
+ if (unlikely(offset > sizeof(*sk)))
+ return -EFAULT;
+
+ *((u32 *)ptr) = val;
+
+ return 0;
+}
Seems strange to me. So, this helper allows to overwrite arbitrary memory
of a struct sock instance. Potentially we could crash the kernel.
And in your sock_filter_convert_ctx_access(), you already implement inline
read/write for the context ...
Your demo code does in pseudocode:
r1 = sk
r2 = offsetof(struct bpf_sock, bound_dev_if)
r3 = idx
r1->sk_bound_dev_if = idx
sock_store_u32(r1, r2, r3) // updates sk_bound_dev_if again to idx
return 1
Dropping that helper from the patch, the only thing a program can do here
is to read/write the sk_bound_dev_if helper per cgroup. Hmm ... dunno. So
this really has to be for cgroups v2, right?
