Commit 5ae437ad authored Feb 19, 2018 by Roman Kapl Committed by David S. Miller Feb 20, 2018

net: sched: report if filter is too large to dump



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 <code@rkapl.cz>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Acked-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent abe27a88

net/sched/cls_api.c

+6 −1

Original line number	Diff line number	Diff line
		@@ -1397,13 +1397,18 @@ 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;
		}

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