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

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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>
This commit is contained in:
Roman Kapl 2018-02-19 21:32:51 +01:00 committed by David S. Miller
parent abe27a885d
commit 5ae437ad5a
1 changed files with 6 additions and 1 deletions
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7
net/sched/cls_api.c
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@ -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;
}