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netfilter: nf_ct_helper: disable automatic helper re-assignment of different type

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This patch modifies __nf_ct_try_assign_helper in a way that invalidates support
for the following scenario:

1) attach the helper A for first time when the conntrack is created
2) attach new (different) helper B due to changes the reply tuple caused by NAT

eg. port redirection from TCP/21 to TCP/5060 with both FTP and SIP helpers
loaded, which seems to be a quite unorthodox scenario.

I can provide a more elaborated patch to support this scenario but explicit
helper attachment provides a better solution for this since now the use can
attach the helpers consistently, without relying on the automatic helper
lookup magic.

This patch fixes a possible out of bound zeroing of the conntrack helper
extension if the helper B uses more memory for its private data than
helper A.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Pablo Neira Ayuso 2012-06-18 17:29:53 +02:00
commit 32f5376003
1 changed files with 7 additions and 1 deletions
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8
net/netfilter/nf_conntrack_helper.c
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@ -229,7 +229,13 @@ int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
goto out; goto out;
} }
} else { } else {
memset(help->data, 0, helper->data_len); /* We only allow helper re-assignment of the same sort since
* we cannot reallocate the helper extension area.
*/
if (help->helper != helper) {
RCU_INIT_POINTER(help->helper, NULL);
goto out;
}
} }
rcu_assign_pointer(help->helper, helper); rcu_assign_pointer(help->helper, helper);