From: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
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@xxxxxxxxxxxxx>
---
net/netfilter/nf_conntrack_helper.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/net/netfilter/nf_conntrack_helper.c b/net/netfilter/nf_conntrack_helper.c
index 2918ec2..c4bc637 100644
--- a/net/netfilter/nf_conntrack_helper.c
+++ b/net/netfilter/nf_conntrack_helper.c
@@ -229,7 +229,13 @@ int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
goto out;
}
} 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);
--
1.7.10
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