So far, if the filter was too large to fit in the allocated skb, the
kernel did not return any error and stopped dumping. Modify the dumper
so that it returns -EMSGSIZE when a filter fails to dump and it is the
first filter in the skb. If we are not first, we will get a next chance
with more room.
I understand this is pretty near to being an API change, but the
original design (silent truncation) can be considered a bug.
Note: The error case can happen pretty easily if you create a filter
with 32 actions and have 4kb pages. Also recent versions of iproute try
to be clever with their buffer allocation size, which in turn leads to
Signed-off-by: Roman Kapl <c...@rkapl.cz>
---
v1 -> v2: add the "progress" comment, fixed error name in commit message.
I've looked at other dumpers in rtnetnlink, there are various ways to handle
that. For example rtnl_stats_dump has:
WARN_ON((err == -EMSGSIZE) && (skb->len == 0));
rtnl_dump_ifinfo has the same logic I am proposing:
if (err < 0)
if (skb->len) goto out;
goto out_err;
Other functions handle the error in the "wrong" way (= what we currently do).
Although it might be OK if there is no array in what they return. I have not
tested the behavior, since the only way I found was to have a device with many
VFs.
net/sched/cls_api.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
index f21610c5da1a..92e9308bb920 100644
--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -1399,13 +1399,18 @@ static int tc_dump_tfilter(struct sk_buff *skb, struct
netlink_callback *cb)
nla_get_u32(tca[TCA_CHAIN]) != chain->index)
continue;
if (!tcf_chain_dump(chain, q, parent, skb, cb,
- index_start, &index))
+ index_start, &index)) {
+ err = -EMSGSIZE;
break;
+ }
}
cb->args[0] = index;
out:
+ /* If we did no progress, the error (EMSGSIZE) is real */
+ if (skb->len == 0 && err)
+ return err;
return skb->len;
}
--
2.16.1
