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netfilter: ctnetlink: fix NULL dereference while trying to change helper 

The patch 1afc56794e03: "netfilter: nf_ct_helper: implement variable
length helper private data" from Jun 7, 2012, leads to the following
Smatch complaint:

net/netfilter/nf_conntrack_netlink.c:1231 ctnetlink_change_helper()
         error: we previously assumed 'help->helper' could be null (see line 1228)

This NULL dereference can be triggered with the following sequence:

1) attach the helper for first time when the conntrack is created.
2) remove the helper module or detach the helper from the conntrack
   via ctnetlink.
3) attach helper again (the same or different one, no matter) to the
   that existing conntrack again via ctnetlink.

This patch fixes the problem by removing the use case that allows you
to re-assign again a helper for one conntrack entry via ctnetlink since
I cannot find any practical use for it.

Change-Id: I67a0a67f6a21f76f869f2f35d3d20225a78dc76e
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Kevin F. Haggerty <haggertk@lineageos.org>
This commit is contained in:
Pablo Neira Ayuso 2012-06-18 17:29:53 +02:00 committed by Francescodario Cuzzocrea
parent 09be4f7a7a
commit ab2638119f
1 changed files with 3 additions and 10 deletions
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13
net/netfilter/nf_conntrack_netlink.c
View File

@ -1213,19 +1213,12 @@ ctnetlink_change_helper(struct nf_conn *ct, const struct nlattr * const cda[])
if (helper->from_nlattr && helpinfo)
helper->from_nlattr(helpinfo, ct);
return 0;
}
if (help->helper)
} else
return -EBUSY;
/* need to zero data of old helper */
memset(help->data, 0, help->helper->data_len);
} else {
/* we cannot set a helper for an existing conntrack */
return -EOPNOTSUPP;
}
rcu_assign_pointer(help->helper, helper);
return 0;
/* we cannot set a helper for an existing conntrack */
return -EOPNOTSUPP;
}
static inline int