linux-kernel - Re: [syzbot] [hams?] possible deadlock in nr_remove

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250208234531.2110-1-hdanton@sina.com>
Date: Sun,  9 Feb 2025 07:45:10 +0800
From: Hillf Danton <hdanton@...a.com>
To: syzbot <syzbot+8863ad36d31449b4dc17@...kaller.appspotmail.com>
Cc: linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [hams?] possible deadlock in nr_remove_neigh (2)

On Fri, 07 Feb 2025 21:02:23 -0800
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    7ee983c850b4 Merge tag 'drm-fixes-2025-02-08' of https://g..
> git tree:       upstream
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17148bdf980000

#syz test

--- x/net/netrom/nr_route.c
+++ y/net/netrom/nr_route.c
@@ -100,6 +100,7 @@ static int __must_check nr_add_node(ax25
 {
 	struct nr_node  *nr_node;
 	struct nr_neigh *nr_neigh;
+	struct nr_neigh *victim = NULL;
 	int i, found;
 	struct net_device *odev;
 
@@ -243,10 +244,9 @@ static int __must_check nr_add_node(ax25
 			/* It must be better than the worst */
 			if (quality > nr_node->routes[2].quality) {
 				nr_node->routes[2].neighbour->count--;
-				nr_neigh_put(nr_node->routes[2].neighbour);
 
 				if (nr_node->routes[2].neighbour->count == 0 && !nr_node->routes[2].neighbour->locked)
-					nr_remove_neigh(nr_node->routes[2].neighbour);
+					victim = nr_node->routes[2].neighbour;
 
 				nr_node->routes[2].quality   = quality;
 				nr_node->routes[2].obs_count = obs_count;
@@ -281,6 +281,8 @@ static int __must_check nr_add_node(ax25
 
 	nr_neigh_put(nr_neigh);
 	nr_node_unlock(nr_node);
+	if (victim)
+		nr_remove_neigh(victim);
 	nr_node_put(nr_node);
 	return 0;
 }
--