net/irda: handle iriap_register_lsap() allocation failure

If iriap_register_lsap() fails to allocate memory, self->lsap is
set to NULL. However, none of the callers handle the failure and
irlmp_connect_request() will happily dereference it:

    iriap_register_lsap: Unable to allocated LSAP!
    ================================================================================
    UBSAN: Undefined behaviour in net/irda/irlmp.c:378:2
    member access within null pointer of type 'struct lsap_cb'
    CPU: 1 PID: 15403 Comm: trinity-c0 Not tainted 4.8.0-rc1+ #81
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.9.3-0-ge2fc41e-prebuilt.qemu-project.org
    04/01/2014
     0000000000000000 ffff88010c7e78a8 ffffffff82344f40 0000000041b58ab3
     ffffffff84f98000 ffffffff82344e94 ffff88010c7e78d0 ffff88010c7e7880
     ffff88010630ad00 ffffffff84a5fae0 ffffffff84d3f5c0 000000000000017a
    Call Trace:
     [<ffffffff82344f40>] dump_stack+0xac/0xfc
     [<ffffffff8242f5a8>] ubsan_epilogue+0xd/0x8a
     [<ffffffff824302bf>] __ubsan_handle_type_mismatch+0x157/0x411
     [<ffffffff83b7bdbc>] irlmp_connect_request+0x7ac/0x970
     [<ffffffff83b77cc0>] iriap_connect_request+0xa0/0x160
     [<ffffffff83b77f48>] state_s_disconnect+0x88/0xd0
     [<ffffffff83b78904>] iriap_do_client_event+0x94/0x120
     [<ffffffff83b77710>] iriap_getvaluebyclass_request+0x3e0/0x6d0
     [<ffffffff83ba6ebb>] irda_find_lsap_sel+0x1eb/0x630
     [<ffffffff83ba90c8>] irda_connect+0x828/0x12d0
     [<ffffffff833c0dfb>] SYSC_connect+0x22b/0x340
     [<ffffffff833c7e09>] SyS_connect+0x9/0x10
     [<ffffffff81007bd3>] do_syscall_64+0x1b3/0x4b0
     [<ffffffff845f946a>] entry_SYSCALL64_slow_path+0x25/0x25
    ================================================================================

The bug seems to have been around since forever.

There's more problems with missing error checks in iriap_init() (and
indeed all of irda_init()), but that's a bigger problem that needs
very careful review and testing. This patch will fix the most serious
bug (as it's easily reached from unprivileged userspace).

I have tested my patch with a reproducer.
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/irda/iriap.c

@@ -185,8 +185,12 @@ struct iriap_cb *iriap_open(__u8 slsap_sel, int mode, void *priv,
 
 	self->magic = IAS_MAGIC;
 	self->mode = mode;
-	if (mode == IAS_CLIENT)
-		iriap_register_lsap(self, slsap_sel, mode);
+	if (mode == IAS_CLIENT) {
+		if (iriap_register_lsap(self, slsap_sel, mode)) {
+			kfree(self);
+			return NULL;
+		}
+	}
 
 	self->confirm = callback;
 	self->priv = priv;