Commit 0f5d82f1 authored Jun 10, 2020 by YiFei Zhu Committed by Daniel Borkmann Jun 11, 2020

net/filter: Permit reading NET in load_bytes_relative when MAC not set



Added a check in the switch case on start_header that checks for
the existence of the header, and in the case that MAC is not set
and the caller requests for MAC, -EFAULT. If the caller requests
for NET then MAC's existence is completely ignored.

There is no function to check NET header's existence and as far
as cgroup_skb/egress is concerned it should always be set.

Removed for ptr >= the start of header, considering offset is
bounded unsigned and should always be true. len <= end - mac is
redundant to ptr + len <= end.

Fixes: 3eee1f75 ("bpf: fix bpf_skb_load_bytes_relative pkt length check")
Signed-off-by: YiFei Zhu <zhuyifei@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/bpf/76bb820ddb6a95f59a772ecbd8c8a336f646b362.1591812755.git.zhuyifei@google.com

parent 47f6bc4c

net/core/filter.c

+9 −7

Original line number	Diff line number	Diff line
		@@ -1755,25 +1755,27 @@ BPF_CALL_5(bpf_skb_load_bytes_relative, const struct sk_buff *, skb,
		u32, offset, void *, to, u32, len, u32, start_header)
		{
		u8 *end = skb_tail_pointer(skb);
		u8 *net = skb_network_header(skb);
		u8 *mac = skb_mac_header(skb);
		u8 *ptr;
		u8 start, ptr;

		if (unlikely(offset > 0xffff \|\| len > (end - mac)))
		if (unlikely(offset > 0xffff))
		goto err_clear;

		switch (start_header) {
		case BPF_HDR_START_MAC:
		ptr = mac + offset;
		if (unlikely(!skb_mac_header_was_set(skb)))
		goto err_clear;
		start = skb_mac_header(skb);
		break;
		case BPF_HDR_START_NET:
		ptr = net + offset;
		start = skb_network_header(skb);
		break;
		default:
		goto err_clear;
		}

		if (likely(ptr >= mac && ptr + len <= end)) {
		ptr = start + offset;

		if (likely(ptr + len <= end)) {
		memcpy(to, ptr, len);
		return 0;
		}

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