Multiple BPF-helpers that can manipulate/increase the size of the SKB uses
__bpf_skb_max_len() as the max-length. This function limit size against
the current net_device MTU (skb->dev->mtu).
When a BPF-prog grow the packet size, then it should not be limited to the
MTU. The MTU is a transmit limitation, and software receiving this packet
should be allowed to increase the size. Further more, current MTU check in
__bpf_skb_max_len uses the MTU from ingress/current net_device, which in
case of redirects uses the wrong net_device.
Keep a sanity max limit of IP_MAX_MTU which is 64KiB.
In later patches we will enforce the MTU limitation when transmitting
packets.
Signed-off-by: Jesper Dangaard Brouer <redacted>
(imported from commit 37f8552786cf46588af52b77829b730dd14524d3)
---
net/core/filter.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/net/core/filter.c b/net/core/filter.c
index 05df73780dd3..fed239e77bdc 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3476,8 +3476,7 @@ static int bpf_skb_net_shrink(struct sk_buff *skb, u32 off, u32 len_diff,
static u32 __bpf_skb_max_len(const struct sk_buff *skb)
{
- return skb->dev ? skb->dev->mtu + skb->dev->hard_header_len :
- SKB_MAX_ALLOC;
+ return IP_MAX_MTU;
}
BPF_CALL_4(sk_skb_adjust_room, struct sk_buff *, skb, s32, len_diff,