s390/iucv: MSG_PEEK causes memory leak in iucv_sock_destruct()

In the Linux kernel, the following vulnerability has been resolved:

s390/iucv: MSG_PEEK causes memory leak in iucv_sock_destruct()

Passing MSG_PEEK flag to skb_recv_datagram() increments skb refcount

(skb->users) and iucv_sock_recvmsg() does not decrement skb refcount

at exit.

This results in skb memory leak in skb_queue_purge() and WARN_ON in

iucv_sock_destruct() during socket close. To fix this decrease

skb refcount by one if MSG_PEEK is set in order to prevent memory

leak and WARN_ON.

WARNING: CPU: 2 PID: 6292 at net/iucv/af_iucv.c:286 iucv_sock_destruct+0x144/0x1a0 [af_iucv]

CPU: 2 PID: 6292 Comm: afiucv_test_msg Kdump: loaded Tainted: G W 6.10.0-rc7 #1

Hardware name: IBM 3931 A01 704 (z/VM 7.3.0)

Call Trace:

[<001587c682c4aa98>] iucv_sock_destruct+0x148/0x1a0 [af_iucv]

[<001587c682c4a9d0>] iucv_sock_destruct+0x80/0x1a0 [af_iucv]

[<001587c704117a32>] __sk_destruct+0x52/0x550

[<001587c704104a54>] __sock_release+0xa4/0x230

[<001587c704104c0c>] sock_close+0x2c/0x40

[<001587c702c5f5a8>] __fput+0x2e8/0x970

[<001587c7024148c4>] task_work_run+0x1c4/0x2c0

[<001587c7023b0716>] do_exit+0x996/0x1050

[<001587c7023b13aa>] do_group_exit+0x13a/0x360

[<001587c7023b1626>] __s390x_sys_exit_group+0x56/0x60

[<001587c7022bccca>] do_syscall+0x27a/0x380

[<001587c7049a6a0c>] __do_syscall+0x9c/0x160

[<001587c7049ce8a8>] system_call+0x70/0x98

Last Breaking-Event-Address:

[<001587c682c4a9d4>] iucv_sock_destruct+0x84/0x1a0 [af_iucv]