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bpf: Check negative offsets in __bpf_skb_min_len()

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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: 5293efe62d ("bpf: add bpf_skb_change_tail helper")
Signed-off-by: Cong Wang <cong.wang@bytedance.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20241213034057.246437-2-xiyou.wangcong@gmail.com
This commit is contained in:
Cong Wang 2024-12-12 19:40:54 -08:00 committed by Daniel Borkmann
parent 5153a75ef3
commit 9ecc4d858b
1 changed files with 15 additions and 6 deletions
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21
net/core/filter.c
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@ -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;
}