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netfilter: Fix potential null pointer dereference

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It's possible for nf_hook_entry_head to return NULL.  If two
nf_unregister_net_hook calls happen simultaneously with a single hook
entry in the list, both will enter the nf_hook_mutex critical section.
The first will successfully delete the head, but the second will see
this NULL pointer and attempt to dereference.

This fix ensures that no null pointer dereference could occur when such
a condition happens.

Fixes: e3b37f11e6 ("netfilter: replace list_head with single linked list")
Signed-off-by: Aaron Conole <aconole@bytheb.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Aaron Conole 2016-09-28 11:35:14 -04:00 committed by Pablo Neira Ayuso
parent 803783849f
commit 5119e4381a
1 changed files with 1 additions and 1 deletions
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2
net/netfilter/core.c
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@ -160,7 +160,7 @@ void nf_unregister_net_hook(struct net *net, const struct nf_hook_ops *reg)
mutex_lock(&nf_hook_mutex);
hooks_entry = nf_hook_entry_head(net, reg);
if (hooks_entry->orig_ops == reg) {
if (hooks_entry && hooks_entry->orig_ops == reg) {
nf_set_hooks_head(net, reg,
nf_entry_dereference(hooks_entry->next));
goto unlock;