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netfilter: nfnetlink_log: cope with concurrent instance destruction

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Instances are refcounted. However, only memory release happens on the
1 -> 0 transition; the unlink from hashes can occur with any refcount.

Uncooperative userspace can force a situation where a queue is pending
for destruction from netlink event while a different socket with same
portid processes an UNBIND request.

With right timing, this will unhash the instance again:

Oops: general protection fault, [..]
Call Trace:
 <TASK>
 nfulnl_recv_config+0x31a/0xd50
 nfnetlink_rcv_msg+0x7c2/0xeb0

Fixes: 0597f2680d ("[NETFILTER]: Add new "nfnetlink_log" userspace packet logging facility")
Reported-by: Eulgyu Kim <eulgyukim@snu.ac.kr>
Reported-by: Jaeyoung Chung <jjy600901@snu.ac.kr>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Florian Westphal 2026-08-25 03:36:03 +02:00 committed by Pablo Neira Ayuso
parent 2c018cc484
commit 387d744fa7
1 changed files with 9 additions and 4 deletions
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13
net/netfilter/nfnetlink_log.c
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@ -228,13 +228,18 @@ static void __nfulnl_flush(struct nfulnl_instance *inst);
static void
__instance_destroy(struct nfulnl_instance *inst)
{
spin_lock(&inst->lock);
if (inst->copy_mode == NFULNL_COPY_DISABLED) {
/* attempt to UNBIND a queue already pending
* destruction via netlink close event. Ignore.
*/
spin_unlock(&inst->lock);
return;
}
/* first pull it out of the global list */
hlist_del_rcu(&inst->hlist);
/* then flush all pending packets from skb */
spin_lock(&inst->lock);
/* lockless readers wont be able to use us */
inst->copy_mode = NFULNL_COPY_DISABLED;