s390/cio: exclude subchannels with no parent from pseudo check

Vasily Gorbik · Vasily Gorbik · commit ab5758848039 · 2019-09-23T23:27:53.000+02:00
ccw console is created early in start_kernel and used before css is initialized or ccw console subchannel is registered. Until then console subchannel does not have a parent. For that reason assume subchannels with no parent are not pseudo subchannels. This fixes the following kasan finding: BUG: KASAN: global-out-of-bounds in sch_is_pseudo_sch+0x8e/0x98 Read of size 8 at addr 00000000000005e8 by task swapper/0/0 CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.3.0-rc8-07370-g6ac43dd12538 #2 Hardware name: IBM 2964 NC9 702 (z/VM 6.4.0) Call Trace: ([<000000000012cd76>] show_stack+0x14e/0x1e0) [<0000000001f7fb44>] dump_stack+0x1a4/0x1f8 [<00000000007d7afc>] print_address_description+0x64/0x3c8 [<00000000007d75f6>] __kasan_report+0x14e/0x180 [<00000000018a2986>] sch_is_pseudo_sch+0x8e/0x98 [<000000000189b950>] cio_enable_subchannel+0x1d0/0x510 [<00000000018cac7c>] ccw_device_recognition+0x12c/0x188 [<0000000002ceb1a8>] ccw_device_enable_console+0x138/0x340 [<0000000002cf1cbe>] con3215_init+0x25e/0x300 [<0000000002c8770a>] console_init+0x68a/0x9b8 [<0000000002c6a3d6>] start_kernel+0x4fe/0x728 [<0000000000100070>] startup_continue+0x70/0xd0 Cc: stable@vger.kernel.org Reviewed-by: Sebastian Ott <sebott@linux.ibm.com> Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
diff --git a/drivers/s390/cio/css.c b/drivers/s390/cio/css.c
@@ -1388,6 +1388,8 @@ device_initcall(cio_settle_init);
 
 int sch_is_pseudo_sch(struct subchannel *sch)
 {
+	if (!sch->dev.parent)
+		return 0;
 	return sch == to_css(sch->dev.parent)->pseudo_subchannel;
 }
 

Original file line number	Diff line number	Diff line change
`@@ -1388,6 +1388,8 @@ device_initcall(cio_settle_init);`
`1388`	`1388`
`1389`	`1389`	`int sch_is_pseudo_sch(struct subchannel *sch)`
`1390`	`1390`	`{`
	`1391`	`+ if (!sch->dev.parent)`
	`1392`	`+ return 0;`
`1391`	`1393`	`return sch == to_css(sch->dev.parent)->pseudo_subchannel;`
`1392`	`1394`	`}`
`1393`	`1395`