On 4/29/21 12:08 PM, Dongseok Yi wrote:
tcp_gso_segment check for the size of GROed payload if it is bigger
than the mss. bpf_skb_proto_6_to_4 increases mss, but the mss can be
bigger than the size of GROed payload unexpectedly if data_len is not
big enough.
Assume that skb gso_size = 1372 and data_len = 8. bpf_skb_proto_6_to_4
would increse the gso_size to 1392. tcp_gso_segment will get an error
with 1380 <= 1392.
Check for the size of GROed payload if it is really bigger than target
mss when increase mss.
Fixes: 6578171a7ff0 (bpf: add bpf_skb_change_proto helper)
Signed-off-by: Dongseok Yi <dseok.yi@xxxxxxxxxxx>
---
net/core/filter.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/net/core/filter.c b/net/core/filter.c
index 9323d34..3f79e3c 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3308,7 +3308,9 @@ static int bpf_skb_proto_6_to_4(struct sk_buff *skb)
}
/* Due to IPv4 header, MSS can be upgraded. */
- skb_increase_gso_size(shinfo, len_diff);
+ if (skb->data_len > len_diff)
Could you elaborate some more on what this has to do with data_len specifically
here? I'm not sure I follow exactly your above commit description. Are you saying
that you're hitting in tcp_gso_segment():
[...]
mss = skb_shinfo(skb)->gso_size;
if (unlikely(skb->len <= mss))
goto out;
[...]
Please provide more context on the bug, thanks!
+ skb_increase_gso_size(shinfo, len_diff);
+
/* Header must be checked, and gso_segs recomputed. */
shinfo->gso_type |= SKB_GSO_DODGY;
shinfo->gso_segs = 0;
