linux-kernel - [PATCH net] netlink: netlink_diag

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Date:   Wed, 02 Nov 2016 20:21:20 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Decotigny <decot@...glers.com>,
        "David S. Miller" <davem@...emloft.net>,
        Dmitry Ivanov <dmitrijs.ivanovs@...t.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Florian Westphal <fw@...len.de>,
        Greg Rose <grose@...htfleet.com>,
        Johannes Berg <johannes.berg@...el.com>,
        Matti Vaittinen <matti.vaittinen@...ia.com>,
        Pravin B Shelar <pshelar@....org>,
        stephen hemminger <stephen@...workplumber.org>,
        Tom Herbert <tom@...bertland.com>,
        Tycho Andersen <tycho.andersen@...onical.com>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        syzkaller <syzkaller@...glegroups.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: [PATCH net] netlink: netlink_diag_dump() runs without locks

From: Eric Dumazet <edumazet@...gle.com>

A recent commit removed locking from netlink_diag_dump() but forgot
one error case.

=====================================
[ BUG: bad unlock balance detected! ]
4.9.0-rc3+ #336 Not tainted
-------------------------------------
syz-executor/4018 is trying to release lock ([   36.220068] nl_table_lock
) at:
[<ffffffff82dc8683>] netlink_diag_dump+0x1a3/0x250 net/netlink/diag.c:182
but there are no more locks to release!

other info that might help us debug this:
3 locks held by syz-executor/4018:
 #0: [   36.220068]  (
sock_diag_mutex[   36.220068] ){+.+.+.}
, at: [   36.220068] [<ffffffff82c3873b>] sock_diag_rcv+0x1b/0x40
 #1: [   36.220068]  (
sock_diag_table_mutex[   36.220068] ){+.+.+.}
, at: [   36.220068] [<ffffffff82c38e00>] sock_diag_rcv_msg+0x140/0x3a0
 #2: [   36.220068]  (
nlk->cb_mutex[   36.220068] ){+.+.+.}
, at: [   36.220068] [<ffffffff82db6600>] netlink_dump+0x50/0xac0

stack backtrace:
CPU: 1 PID: 4018 Comm: syz-executor Not tainted 4.9.0-rc3+ #336
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
 ffff8800645df688 ffffffff81b46934 ffffffff84eb3e78 ffff88006ad85800
 ffffffff82dc8683 ffffffff84eb3e78 ffff8800645df6b8 ffffffff812043ca
 dffffc0000000000 ffff88006ad85ff8 ffff88006ad85fd0 00000000ffffffff
Call Trace:
 [<     inline     >] __dump_stack lib/dump_stack.c:15
 [<ffffffff81b46934>] dump_stack+0xb3/0x10f lib/dump_stack.c:51
 [<ffffffff812043ca>] print_unlock_imbalance_bug+0x17a/0x1a0
kernel/locking/lockdep.c:3388
 [<     inline     >] __lock_release kernel/locking/lockdep.c:3512
 [<ffffffff8120cfd8>] lock_release+0x8e8/0xc60 kernel/locking/lockdep.c:3765
 [<     inline     >] __raw_read_unlock ./include/linux/rwlock_api_smp.h:225
 [<ffffffff83fc001a>] _raw_read_unlock+0x1a/0x30 kernel/locking/spinlock.c:255
 [<ffffffff82dc8683>] netlink_diag_dump+0x1a3/0x250 net/netlink/diag.c:182
 [<ffffffff82db6947>] netlink_dump+0x397/0xac0 net/netlink/af_netlink.c:2110


Fixes: ad202074320c ("netlink: Use rhashtable walk interface in diag dump")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Reported-by: Andrey Konovalov <andreyknvl@...gle.com>
Tested-by: Andrey Konovalov <andreyknvl@...gle.com>
---
 net/netlink/diag.c |    5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/net/netlink/diag.c b/net/netlink/diag.c
index b2f0e986a6f4..a5546249fb10 100644
--- a/net/netlink/diag.c
+++ b/net/netlink/diag.c
@@ -178,11 +178,8 @@ static int netlink_diag_dump(struct sk_buff *skb, struct netlink_callback *cb)
 		}
 		cb->args[1] = i;
 	} else {
-		if (req->sdiag_protocol >= MAX_LINKS) {
-			read_unlock(&nl_table_lock);
-			rcu_read_unlock();
+		if (req->sdiag_protocol >= MAX_LINKS)
 			return -ENOENT;
-		}
 
 		err = __netlink_diag_dump(skb, cb, req->sdiag_protocol, s_num);
 	}