Commit 4b9adb8d authored Jun 21, 2023 by Eric Dumazet Committed by Greg Kroah-Hartman Aug 11, 2023

netlink: fix potential deadlock in netlink_set_err()



[ Upstream commit 8d61f926d42045961e6b65191c09e3678d86a9cf ]

syzbot reported a possible deadlock in netlink_set_err() [1]

A similar issue was fixed in commit 1d482e666b8e ("netlink: disable IRQs
for netlink_lock_table()") in netlink_lock_table()

This patch adds IRQ safety to netlink_set_err() and __netlink_diag_dump()
which were not covered by cited commit.

[1]

WARNING: possible irq lock inversion dependency detected
6.4.0-rc6-syzkaller-00240-g4e9f0ec38852 #0 Not tainted

syz-executor.2/23011 just changed the state of lock:
ffffffff8e1a7a58 (nl_table_lock){.+.?}-{2:2}, at: netlink_set_err+0x2e/0x3a0 net/netlink/af_netlink.c:1612
but this lock was taken by another, SOFTIRQ-safe lock in the past:
 (&local->queue_stop_reason_lock){..-.}-{2:2}

and interrupts could create inverse lock ordering between them.

other info that might help us debug this:
 Possible interrupt unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(nl_table_lock);
                               local_irq_disable();
                               lock(&local->queue_stop_reason_lock);
                               lock(nl_table_lock);
  <Interrupt>
    lock(&local->queue_stop_reason_lock);

 *** DEADLOCK ***

Fixes: 1d482e666b8e ("netlink: disable IRQs for netlink_lock_table()")
Reported-by:  <syzbot+a7d200a347f912723e5c@syzkaller.appspotmail.com>
Link: https://syzkaller.appspot.com/bug?extid=a7d200a347f912723e5c
Link: https://lore.kernel.org/netdev/000000000000e38d1605fea5747e@google.com/T/#u


Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Johannes Berg <johannes.berg@intel.com>
Link: https://lore.kernel.org/r/20230621154337.1668594-1-edumazet@google.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

parent b9d02ca2

net/netlink/af_netlink.c

+3 −2

Original line number	Diff line number	Diff line
		@@ -1603,6 +1603,7 @@ static int do_one_set_err(struct sock sk, struct netlink_set_err_data p)
		int netlink_set_err(struct sock *ssk, u32 portid, u32 group, int code)
		{
		struct netlink_set_err_data info;
		unsigned long flags;
		struct sock *sk;
		int ret = 0;

		@@ -1612,12 +1613,12 @@ int netlink_set_err(struct sock *ssk, u32 portid, u32 group, int code)
		/* sk->sk_err wants a positive error value */
		info.code = -code;

		read_lock(&nl_table_lock);
		read_lock_irqsave(&nl_table_lock, flags);

		sk_for_each_bound(sk, &nl_table[ssk->sk_protocol].mc_list)
		ret += do_one_set_err(sk, &info);

		read_unlock(&nl_table_lock);
		read_unlock_irqrestore(&nl_table_lock, flags);
		return ret;
		}
		EXPORT_SYMBOL(netlink_set_err);

net/netlink/diag.c

+3 −2

Original line number	Diff line number	Diff line
		@@ -93,6 +93,7 @@ static int __netlink_diag_dump(struct sk_buff skb, struct netlink_callback cb,
		struct net *net = sock_net(skb->sk);
		struct netlink_diag_req *req;
		struct netlink_sock *nlsk;
		unsigned long flags;
		struct sock *sk;
		int num = 2;
		int ret = 0;
		@@ -151,7 +152,7 @@ static int __netlink_diag_dump(struct sk_buff skb, struct netlink_callback cb,
		num++;

		mc_list:
		read_lock(&nl_table_lock);
		read_lock_irqsave(&nl_table_lock, flags);
		sk_for_each_bound(sk, &tbl->mc_list) {
		if (sk_hashed(sk))
		continue;
		@@ -172,7 +173,7 @@ static int __netlink_diag_dump(struct sk_buff skb, struct netlink_callback cb,
		}
		num++;
		}
		read_unlock(&nl_table_lock);
		read_unlock_irqrestore(&nl_table_lock, flags);

		done:
		cb->args[0] = num;