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@xxxxxxxx>
Fixes: 6578171a7ff0 ("bpf: add bpf_skb_change_proto helper")
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
---
CC: daniel@xxxxxxxxxxxxx
CC: martin.lau@xxxxxxxxx
CC: song@xxxxxxxxxx
CC: john.fastabend@xxxxxxxxx
CC: sdf@xxxxxxxxxx
CC: bpf@xxxxxxxxxxxxxxx
---
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 929358677183..43cc1fe58a2c 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3180,15 +3180,18 @@ 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;
}
--
2.38.1
