linux-kernel - Re: [syzbot] [net?] possible deadlock in unix_del

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Message-ID: <20240405052841.97772-1-kuniyu@amazon.com>
Date: Thu, 4 Apr 2024 22:28:41 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <syzbot+7f7f201cc2668a8fd169@...kaller.appspotmail.com>
CC: <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
	<linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>,
	<pabeni@...hat.com>, <syzkaller-bugs@...glegroups.com>, <kuniyu@...zon.com>
Subject: Re: [syzbot] [net?] possible deadlock in unix_del_edges

From: syzbot <syzbot+7f7f201cc2668a8fd169@...kaller.appspotmail.com>
Date: Thu, 04 Apr 2024 09:13:26 -0700
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    2b3d5988ae2c Add linux-next specific files for 20240404
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=13114d8d180000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=9c48fd2523cdee5e
> dashboard link: https://syzkaller.appspot.com/bug?extid=7f7f201cc2668a8fd169
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=113c7103180000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1133aaa9180000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/136270ed2c7b/disk-2b3d5988.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/466d2f7c1952/vmlinux-2b3d5988.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/7dfaf3959891/bzImage-2b3d5988.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+7f7f201cc2668a8fd169@...kaller.appspotmail.com

The boot failure for the previous patch is not related to the patch.
Probably I should've specified the gc commit.

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git 4090fa373f0e763c43610853d2774b5979915959

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 61ecfa9c9c6b..d3bf9f49012d 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -2619,7 +2619,9 @@ static struct sk_buff *manage_oob(struct sk_buff *skb, struct sock *sk,
 				}
 			} else if (!(flags & MSG_PEEK)) {
 				skb_unlink(skb, &sk->sk_receive_queue);
-				consume_skb(skb);
+				WRITE_ONCE(u->oob_skb, NULL);
+				kfree_skb(skb);
+				kfree_skb(skb);
 				skb = skb_peek(&sk->sk_receive_queue);
 			}
 		}