linux-kernel - net/unix/af_unix.c:2471 manage_oob() warn: returning freed memory 'skb'

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Date:   Tue, 12 Jul 2022 11:57:48 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     kbuild@...ts.01.org, Rao Shoaib <rao.shoaib@...cle.com>
Cc:     lkp@...el.com, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org
Subject: net/unix/af_unix.c:2471 manage_oob() warn: returning freed memory
 'skb'

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   e8a4e1c1bb697b1d9fc48f0e56dc0f50bc024bee
commit: 314001f0bf927015e459c9d387d62a231fe93af3 af_unix: Add OOB support
config: m68k-randconfig-m031-20220708 (https://download.01.org/0day-ci/archive/20220709/202207090117.Ub3gbT5M-lkp@intel.com/config)
compiler: m68k-linux-gcc (GCC) 11.3.0

If you fix the issue, kindly add following tag where applicable
Reported-by: kernel test robot <lkp@...el.com>
Reported-by: Dan Carpenter <dan.carpenter@...cle.com>

smatch warnings:
net/unix/af_unix.c:2471 manage_oob() warn: returning freed memory 'skb'

vim +/skb +2471 net/unix/af_unix.c

314001f0bf9270 Rao Shoaib 2021-08-01  2446  static struct sk_buff *manage_oob(struct sk_buff *skb, struct sock *sk,
314001f0bf9270 Rao Shoaib 2021-08-01  2447  				  int flags, int copied)
314001f0bf9270 Rao Shoaib 2021-08-01  2448  {
314001f0bf9270 Rao Shoaib 2021-08-01  2449  	struct unix_sock *u = unix_sk(sk);
314001f0bf9270 Rao Shoaib 2021-08-01  2450  
314001f0bf9270 Rao Shoaib 2021-08-01  2451  	if (!unix_skb_len(skb) && !(flags & MSG_PEEK)) {
314001f0bf9270 Rao Shoaib 2021-08-01  2452  		skb_unlink(skb, &sk->sk_receive_queue);
314001f0bf9270 Rao Shoaib 2021-08-01  2453  		consume_skb(skb);
314001f0bf9270 Rao Shoaib 2021-08-01  2454  		skb = NULL;
314001f0bf9270 Rao Shoaib 2021-08-01  2455  	} else {
314001f0bf9270 Rao Shoaib 2021-08-01  2456  		if (skb == u->oob_skb) {
314001f0bf9270 Rao Shoaib 2021-08-01  2457  			if (copied) {
314001f0bf9270 Rao Shoaib 2021-08-01  2458  				skb = NULL;
314001f0bf9270 Rao Shoaib 2021-08-01  2459  			} else if (sock_flag(sk, SOCK_URGINLINE)) {
314001f0bf9270 Rao Shoaib 2021-08-01  2460  				if (!(flags & MSG_PEEK)) {
314001f0bf9270 Rao Shoaib 2021-08-01  2461  					u->oob_skb = NULL;
314001f0bf9270 Rao Shoaib 2021-08-01  2462  					consume_skb(skb);

It's so weird that we're sending warnings about 2021 code...  I looked
at this warning on Aug 10, 2021 but for some reason I didn't send it.

314001f0bf9270 Rao Shoaib 2021-08-01  2463  				}
314001f0bf9270 Rao Shoaib 2021-08-01  2464  			} else if (!(flags & MSG_PEEK)) {
314001f0bf9270 Rao Shoaib 2021-08-01  2465  				skb_unlink(skb, &sk->sk_receive_queue);
314001f0bf9270 Rao Shoaib 2021-08-01  2466  				consume_skb(skb);
314001f0bf9270 Rao Shoaib 2021-08-01  2467  				skb = skb_peek(&sk->sk_receive_queue);
314001f0bf9270 Rao Shoaib 2021-08-01  2468  			}
314001f0bf9270 Rao Shoaib 2021-08-01  2469  		}
314001f0bf9270 Rao Shoaib 2021-08-01  2470  	}
314001f0bf9270 Rao Shoaib 2021-08-01 @2471  	return skb;
314001f0bf9270 Rao Shoaib 2021-08-01  2472  }

-- 
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