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Subject[PATCH 4.15 048/122] net: sched: report if filter is too large to dump
Date
4.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Roman Kapl <code@rkapl.cz>


[ Upstream commit 5ae437ad5a2ed573b1ebb04e0afa70b8869f88dd ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/sched/cls_api.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -1054,13 +1054,18 @@ static int tc_dump_tfilter(struct sk_buf
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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