Commit ab21c1b5 authored Oct 24, 2018 by Daniel Borkmann Committed by Alexei Starovoitov Oct 25, 2018

bpf: disallow direct packet access for unpriv in cg_skb



Commit b39b5f41 ("bpf: add cg_skb_is_valid_access for
BPF_PROG_TYPE_CGROUP_SKB") added support for returning pkt pointers
for direct packet access. Given this program type is allowed for both
unprivileged and privileged users, we shouldn't allow unprivileged
ones to use it, e.g. besides others one reason would be to avoid any
potential speculation on the packet test itself, thus guard this for
root only.

Fixes: b39b5f41 ("bpf: add cg_skb_is_valid_access for BPF_PROG_TYPE_CGROUP_SKB")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Cc: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

parent 36641ad6

net/core/filter.c

+6 −0

Original line number	Diff line number	Diff line
		@@ -5496,7 +5496,13 @@ static bool cg_skb_is_valid_access(int off, int size,
		case bpf_ctx_range(struct __sk_buff, data_meta):
		case bpf_ctx_range(struct __sk_buff, flow_keys):
		return false;
		case bpf_ctx_range(struct __sk_buff, data):
		case bpf_ctx_range(struct __sk_buff, data_end):
		if (!capable(CAP_SYS_ADMIN))
		return false;
		break;
		}

		if (type == BPF_WRITE) {
		switch (off) {
		case bpf_ctx_range(struct __sk_buff, mark):

tools/testing/selftests/bpf/test_verifier.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -4892,7 +4892,7 @@ static struct bpf_test tests[] = {
		},
		.result = ACCEPT,
		.result_unpriv = REJECT,
		.errstr_unpriv = "R3 pointer comparison prohibited",
		.errstr_unpriv = "invalid bpf_context access off=76 size=4",
		.prog_type = BPF_PROG_TYPE_CGROUP_SKB,
		},
		{

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