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netfilter: nf_ct_helper: disable automatic helper re-assignment of different type
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>
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1 changed files with 7 additions and 1 deletions
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@ -229,7 +229,13 @@ int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
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goto out;
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}
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} else {
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memset(help->data, 0, helper->data_len);
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/* We only allow helper re-assignment of the same sort since
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* we cannot reallocate the helper extension area.
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*/
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if (help->helper != helper) {
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RCU_INIT_POINTER(help->helper, NULL);
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goto out;
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}
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}
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rcu_assign_pointer(help->helper, helper);
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