On 10/8/24 7:33 AM, Cong Wang wrote:
From: Cong Wang <cong.wang@xxxxxxxxxxxxx>
skb_transport_offset() and skb_transport_offset() can be negative when
nit: I presume the 2nd one is skb_network_offset?
they are called after we pull the transport header, for example, when
we use eBPF sockmap (aka 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 causes bpf_skb_change_tail() failed
unexpectedly.
Fix this by using a signed int to get these offsets and test them
against zero.
Fixes: 5293efe62df8 ("bpf: add bpf_skb_change_tail helper")
Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Signed-off-by: Cong Wang <cong.wang@xxxxxxxxxxxxx>
Is there any chance you could also extend the sockmap BPF selftest with
this case you're hitting so that BPF CI can run this regularly?
---
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 4e3f42cc6611..10ef27639a5d 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3737,13 +3737,22 @@ 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;
I'll let John chime in, but does this mean in case of sockmap min_len always ends
up at 0? I just wonder whether we should pass a custom __bpf_skb_min_len to
__bpf_skb_change_tail for bpf_skb_change_tail vs sk_skb_change_tail assuming the
compiler is able to inlining all this (instead of indirect call).
