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Subject[PATCH 4.14 043/110] net: sched: report if filter is too large to dump
4.14-stable review patch.  If anyone has any objections, please let me know.


From: Roman Kapl <>

[ 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 <>
Acked-by: Jiri Pirko <>
Acked-by: Cong Wang <>
Signed-off-by: David S. Miller <>
Signed-off-by: Greg Kroah-Hartman <>
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
@@ -871,13 +871,18 @@ static int tc_dump_tfilter(struct sk_buf
if (tca[TCA_CHAIN] &&
nla_get_u32(tca[TCA_CHAIN]) != chain->index)
- if (!tcf_chain_dump(chain, skb, cb, index_start, &index))
+ if (!tcf_chain_dump(chain, skb, cb, index_start, &index)) {
+ err = -EMSGSIZE;
+ }

cb->args[0] = index;

+ /* If we did no progress, the error (EMSGSIZE) is real */
+ if (skb->len == 0 && err)
+ return err;
return skb->len;

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