From: Jakub Kicinski kuba@kernel.org
[ Upstream commit 54c3f1a81421f85e60ae2eaae7be3727a09916ee ]
Anand hit a BUG() when pulling off headers on egress to a SW tunnel. We get to skb_checksum_help() with an invalid checksum offset (commit d7ea0d9df2a6 ("net: remove two BUG() from skb_checksum_help()") converted those BUGs to WARN_ONs()). He points out oddness in how skb_postpull_rcsum() gets used. Indeed looks like we should pull before "postpull", otherwise the CHECKSUM_PARTIAL fixup from skb_postpull_rcsum() will not be able to do its job:
if (skb->ip_summed == CHECKSUM_PARTIAL && skb_checksum_start_offset(skb) < 0) skb->ip_summed = CHECKSUM_NONE;
Reported-by: Anand Parthasarathy anpartha@meta.com Fixes: 6578171a7ff0 ("bpf: add bpf_skb_change_proto helper") Signed-off-by: Jakub Kicinski kuba@kernel.org Acked-by: Stanislav Fomichev sdf@google.com Link: https://lore.kernel.org/r/20221220004701.402165-1-kuba@kernel.org Signed-off-by: Martin KaFai Lau martin.lau@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/core/filter.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/net/core/filter.c b/net/core/filter.c index 0613aa7b0966..29d85a20f4fc 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -2035,15 +2035,18 @@ static int bpf_skb_generic_push(struct sk_buff *skb, u32 off, u32 len)
static int bpf_skb_generic_pop(struct sk_buff *skb, u32 off, u32 len) { + void *old_data; + /* skb_ensure_writable() is not needed here, as we're * already working on an uncloned skb. */ if (unlikely(!pskb_may_pull(skb, off + len))) return -ENOMEM;
- skb_postpull_rcsum(skb, skb->data + off, len); - memmove(skb->data + len, skb->data, off); + old_data = skb->data; __skb_pull(skb, len); + skb_postpull_rcsum(skb, old_data + off, len); + memmove(skb->data, old_data, off);
return 0; }