net: neighbour: prohibit negative value for unres_qlen_bytes parameter
authorShan Wei <davidshan@tencent.com>
Tue, 4 Dec 2012 18:49:15 +0000 (18:49 +0000)
committerDavid S. Miller <davem@davemloft.net>
Wed, 5 Dec 2012 21:01:28 +0000 (16:01 -0500)
commitce46cc64d47a8afaf13c300b09a7f9c29f4979b6
tree2fcaf39d15b41ee1f92f14eb8035f82eb80a5364
parent1642182ea0eedecc5d6f330c43cef8639327f0e5
net: neighbour: prohibit negative value for unres_qlen_bytes parameter

unres_qlen_bytes and unres_qlen are int type.
But multiple relation(unres_qlen_bytes = unres_qlen * SKB_TRUESIZE(ETH_FRAME_LEN))
will cause type overflow when seting unres_qlen. e.g.

$ echo 1027506 > /proc/sys/net/ipv4/neigh/eth1/unres_qlen
$ cat /proc/sys/net/ipv4/neigh/eth1/unres_qlen
1182657265
$ cat /proc/sys/net/ipv4/neigh/eth1/unres_qlen_bytes
-2147479756

The gutted value is not that we setting。
But user/administrator don't know this is caused by int type overflow.

what's more, it is meaningless and even dangerous that unres_qlen_bytes is set
with negative number. Because, for unresolved neighbour address, kernel will cache packets
without limit in __neigh_event_send()(e.g. (u32)-1 = 2GB).

Signed-off-by: Shan Wei <davidshan@tencent.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
net/core/neighbour.c