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netfilter: ctnetlink: make it safer when checking the ct helper name

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One CPU is doing ctnetlink_change_helper(), while another CPU is doing
unhelp() at the same time. So even if help->helper is not NULL at first,
the later statement strcmp(help->helper->name, ...) may still access
the NULL pointer.

So we must use rcu_read_lock and rcu_dereference to avoid such _bad_
thing happen.

Fixes: f95d7a46bc ("netfilter: ctnetlink: Fix regression in CTA_HELP processing")
Signed-off-by: Liping Zhang <zlpnobody@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Liping Zhang 2017-04-01 20:55:44 +08:00 committed by Pablo Neira Ayuso
parent 8b5995d063
commit 3173d5b8c8
1 changed files with 10 additions and 5 deletions
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15
net/netfilter/nf_conntrack_netlink.c
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@ -1488,11 +1488,16 @@ static int ctnetlink_change_helper(struct nf_conn *ct,
* treat the second attempt as a no-op instead of returning
* an error.
*/
if (help && help->helper &&
!strcmp(help->helper->name, helpname))
return 0;
else
return -EBUSY;
err = -EBUSY;
if (help) {
rcu_read_lock();
helper = rcu_dereference(help->helper);
if (helper && !strcmp(helper->name, helpname))
err = 0;
rcu_read_unlock();
}
return err;
}
if (!strcmp(helpname, "")) {