From 0f5d82f187e1beda3fe7295dfc500af266a5bd80 Mon Sep 17 00:00:00 2001 From: YiFei Zhu Date: Wed, 10 Jun 2020 13:41:39 -0500 Subject: 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: 3eee1f75f2b9 ("bpf: fix bpf_skb_load_bytes_relative pkt length check") Signed-off-by: YiFei Zhu Signed-off-by: Daniel Borkmann Reviewed-by: Stanislav Fomichev Link: https://lore.kernel.org/bpf/76bb820ddb6a95f59a772ecbd8c8a336f646b362.1591812755.git.zhuyifei@google.com --- net/core/filter.c | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-) diff --git a/net/core/filter.c b/net/core/filter.c index 90d2eb77002f..1b7d1180931c 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -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; } -- cgit v1.2.3