Vulnerability: An issue was discovered in the Linux kernel before 5.0. The function __mdiobus_register() in drivers/net/phy/mdio_bus.c calls put_device(), which will trigger a fixed_mdio_bus_init use-after-free. This will cause a denial of service.
Vulnerability ID: CVE-2019-12819
CWE: CWE-416
Severity score: 2.9
Project: https://github.com/torvalds/linux
Published: 2019-06-14
File: drivers/net/phy/mdio_bus.c
Commit message: mdio_bus: Fix use-after-free on device_register fails

KASAN has found use-after-free in fixed_mdio_bus_init,
commit 0c692d07842a ("drivers/net/phy/mdio_bus.c: call
put_device on device_register() failure") call put_device()
while device_register() fails,give up the last reference
to the device and allow mdiobus_release to be executed
,kfreeing the bus. However in most drives, mdiobus_free
be called to free the bus while mdiobus_register fails.
use-after-free occurs when access bus again, this patch
revert it to let mdiobus_free free the bus.

KASAN report details as below:

BUG: KASAN: use-after-free in mdiobus_free+0x85/0x90 drivers/net/phy/mdio_bus.c:482
Read of size 4 at addr ffff8881dc824d78 by task syz-executor.0/3524

CPU: 1 PID: 3524 Comm: syz-executor.0 Not tainted 5.0.0-rc7+ #45
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0xfa/0x1ce lib/dump_stack.c:113
 print_address_description+0x65/0x270 mm/kasan/report.c:187
 kasan_report+0x149/0x18d mm/kasan/report.c:317
 mdiobus_free+0x85/0x90 drivers/net/phy/mdio_bus.c:482
 fixed_mdio_bus_init+0x283/0x1000 [fixed_phy]
 ? 0xffffffffc0e40000
 ? 0xffffffffc0e40000
 ? 0xffffffffc0e40000
 do_one_initcall+0xfa/0x5ca init/main.c:887
 do_init_module+0x204/0x5f6 kernel/module.c:3460
 load_module+0x66b2/0x8570 kernel/module.c:3808
 __do_sys_finit_module+0x238/0x2a0 kernel/module.c:3902
 do_syscall_64+0x147/0x600 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x462e99
Code: f7 d8 64 89 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f6215c19c58 EFLAGS: 00000246 ORIG_RAX: 0000000000000139
RAX: ffffffffffffffda RBX: 000000000073bf00 RCX: 0000000000462e99
RDX: 0000000000000000 RSI: 0000000020000080 RDI: 0000000000000003
RBP: 00007f6215c19c70 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f6215c1a6bc
R13: 00000000004bcefb R14: 00000000006f7030 R15: 0000000000000004

Allocated by task 3524:
 set_track mm/kasan/common.c:85 [inline]
 __kasan_kmalloc.constprop.3+0xa0/0xd0 mm/kasan/common.c:496
 kmalloc include/linux/slab.h:545 [inline]
 kzalloc include/linux/slab.h:740 [inline]
 mdiobus_alloc_size+0x54/0x1b0 drivers/net/phy/mdio_bus.c:143
 fixed_mdio_bus_init+0x163/0x1000 [fixed_phy]
 do_one_initcall+0xfa/0x5ca init/main.c:887
 do_init_module+0x204/0x5f6 kernel/module.c:3460
 load_module+0x66b2/0x8570 kernel/module.c:3808
 __do_sys_finit_module+0x238/0x2a0 kernel/module.c:3902
 do_syscall_64+0x147/0x600 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 3524:
 set_track mm/kasan/common.c:85 [inline]
 __kasan_slab_free+0x130/0x180 mm/kasan/common.c:458
 slab_free_hook mm/slub.c:1409 [inline]
 slab_free_freelist_hook mm/slub.c:1436 [inline]
 slab_free mm/slub.c:2986 [inline]
 kfree+0xe1/0x270 mm/slub.c:3938
 device_release+0x78/0x200 drivers/base/core.c:919
 kobject_cleanup lib/kobject.c:662 [inline]
 kobject_release lib/kobject.c:691 [inline]
 kref_put include/linux/kref.h:67 [inline]
 kobject_put+0x146/0x240 lib/kobject.c:708
 put_device+0x1c/0x30 drivers/base/core.c:2060
 __mdiobus_register+0x483/0x560 drivers/net/phy/mdio_bus.c:382
 fixed_mdio_bus_init+0x26b/0x1000 [fixed_phy]
 do_one_initcall+0xfa/0x5ca init/main.c:887
 do_init_module+0x204/0x5f6 kernel/module.c:3460
 load_module+0x66b2/0x8570 kernel/module.c:3808
 __do_sys_finit_module+0x238/0x2a0 kernel/module.c:3902
 do_syscall_64+0x147/0x600 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8881dc824c80
 which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 248 bytes inside of
 2048-byte region [ffff8881dc824c80, ffff8881dc825480)
The buggy address belongs to the page:
page:ffffea0007720800 count:1 mapcount:0 mapping:ffff8881f6c02800 index:0x0 compound_mapcount: 0
flags: 0x2fffc0000010200(slab|head)
raw: 02fffc0000010200 0000000000000000 0000000500000001 ffff8881f6c02800
raw: 0000000000000000 00000000800f000f 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8881dc824c00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8881dc824c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8881dc824d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                                ^
 ffff8881dc824d80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8881dc824e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

Fixes: 0c692d07842a ("drivers/net/phy/mdio_bus.c: call put_device on device_register() failure")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
Commit author: YueHaibing

Vulnerable version (before fix):
 int __mdiobus_register(struct mii_bus *bus, struct module *owner) 	err = device_register(&bus->dev); 	if (err) { 		pr_err("mii_bus %s failed to register\n", bus->id); 		put_device(&bus->dev); 		return -EINVAL; 	} 

Fixed version (after fix):
 int __mdiobus_register(struct mii_bus *bus, struct module *owner) 	err = device_register(&bus->dev); 	if (err) { 		pr_err("mii_bus %s failed to register\n", bus->id); 		return -EINVAL; 	} 

Patch:
patch: @@ -379,7 +379,6 @@ int __mdiobus_register(struct mii_bus *bus, struct module *owner)
 	err = device_register(&bus->dev);
 	if (err) {
 		pr_err("mii_bus %s failed to register\n", bus->id);
-		put_device(&bus->dev);
 		return -EINVAL;
 	}
path: drivers/net/phy/mdio_bus.c