From 9ecc4d858b92c1bb0673ad9c327298e600c55659 Mon Sep 17 00:00:00 2001 From: Cong Wang Date: Thu, 12 Dec 2024 19:40:54 -0800 Subject: [PATCH] bpf: Check negative offsets in __bpf_skb_min_len() skb_network_offset() and skb_transport_offset() can be negative when they are called after we pull the transport header, for example, when we use eBPF sockmap at the point of ->sk_data_ready(). __bpf_skb_min_len() uses an unsigned int to get these offsets, this leads to a very large number which then causes bpf_skb_change_tail() failed unexpectedly. Fix this by using a signed int to get these offsets and ensure the minimum is at least zero. Fixes: 5293efe62df8 ("bpf: add bpf_skb_change_tail helper") Signed-off-by: Cong Wang Signed-off-by: Daniel Borkmann Acked-by: John Fastabend Link: https://lore.kernel.org/bpf/20241213034057.246437-2-xiyou.wangcong@gmail.com --- net/core/filter.c | 21 +++++++++++++++------ 1 file changed, 15 insertions(+), 6 deletions(-) diff --git a/net/core/filter.c b/net/core/filter.c index 21131ec25f24..834614071727 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -3734,13 +3734,22 @@ static const struct bpf_func_proto bpf_skb_adjust_room_proto = { static u32 __bpf_skb_min_len(const struct sk_buff *skb) { - u32 min_len = skb_network_offset(skb); + int offset = skb_network_offset(skb); + u32 min_len = 0; - if (skb_transport_header_was_set(skb)) - min_len = skb_transport_offset(skb); - if (skb->ip_summed == CHECKSUM_PARTIAL) - min_len = skb_checksum_start_offset(skb) + - skb->csum_offset + sizeof(__sum16); + if (offset > 0) + min_len = offset; + if (skb_transport_header_was_set(skb)) { + offset = skb_transport_offset(skb); + if (offset > 0) + min_len = offset; + } + if (skb->ip_summed == CHECKSUM_PARTIAL) { + offset = skb_checksum_start_offset(skb) + + skb->csum_offset + sizeof(__sum16); + if (offset > 0) + min_len = offset; + } return min_len; }