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Commit 9777d12a authored by YiFei Zhu's avatar YiFei Zhu Committed by Greg Kroah-Hartman
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net/filter: Permit reading NET in load_bytes_relative when MAC not set 



[ Upstream commit 0f5d82f187e1beda3fe7295dfc500af266a5bd80 ]

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: default avatarYiFei Zhu <zhuyifei@google.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Reviewed-by: default avatarStanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/bpf/76bb820ddb6a95f59a772ecbd8c8a336f646b362.1591812755.git.zhuyifei@google.com


Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 0eb4e157

net/core/filter.c

+9 −7
Original line number Diff line number Diff line
@@ -1766,25 +1766,27 @@ 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;

	}