workqueue, lockdep: Fix an alloc_workqueue() error path

This patch fixes a use-after-free and a memory leak in an alloc_workqueue()
error path.

Repoted by syzkaller and KASAN:

  BUG: KASAN: use-after-free in __read_once_size include/linux/compiler.h:197 [inline]
  BUG: KASAN: use-after-free in lockdep_register_key+0x3b9/0x490 kernel/locking/lockdep.c:1023
  Read of size 8 at addr ffff888090fc2698 by task syz-executor134/7858

  CPU: 1 PID: 7858 Comm: syz-executor134 Not tainted 5.0.0-rc8-next-20190301 #1
  Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
  Call Trace:
   __dump_stack lib/dump_stack.c:77 [inline]
   dump_stack+0x172/0x1f0 lib/dump_stack.c:113
   print_address_description.cold+0x7c/0x20d mm/kasan/report.c:187
   kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317
   __asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:132
   __read_once_size include/linux/compiler.h:197 [inline]
   lockdep_register_key+0x3b9/0x490 kernel/locking/lockdep.c:1023
   wq_init_lockdep kernel/workqueue.c:3444 [inline]
   alloc_workqueue+0x427/0xe70 kernel/workqueue.c:4263
   ucma_open+0x76/0x290 drivers/infiniband/core/ucma.c:1732
   misc_open+0x398/0x4c0 drivers/char/misc.c:141
   chrdev_open+0x247/0x6b0 fs/char_dev.c:417
   do_dentry_open+0x488/0x1160 fs/open.c:771
   vfs_open+0xa0/0xd0 fs/open.c:880
   do_last fs/namei.c:3416 [inline]
   path_openat+0x10e9/0x46e0 fs/namei.c:3533
   do_filp_open+0x1a1/0x280 fs/namei.c:3563
   do_sys_open+0x3fe/0x5d0 fs/open.c:1063
   __do_sys_openat fs/open.c:1090 [inline]
   __se_sys_openat fs/open.c:1084 [inline]
   __x64_sys_openat+0x9d/0x100 fs/open.c:1084
   do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
   entry_SYSCALL_64_after_hwframe+0x49/0xbe

  Allocated by task 7789:
   save_stack+0x45/0xd0 mm/kasan/common.c:75
   set_track mm/kasan/common.c:87 [inline]
   __kasan_kmalloc mm/kasan/common.c:497 [inline]
   __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:470
   kasan_kmalloc+0x9/0x10 mm/kasan/common.c:511
   __do_kmalloc mm/slab.c:3726 [inline]
   __kmalloc+0x15c/0x740 mm/slab.c:3735
   kmalloc include/linux/slab.h:553 [inline]
   kzalloc include/linux/slab.h:743 [inline]
   alloc_workqueue+0x13c/0xe70 kernel/workqueue.c:4236
   ucma_open+0x76/0x290 drivers/infiniband/core/ucma.c:1732
   misc_open+0x398/0x4c0 drivers/char/misc.c:141
   chrdev_open+0x247/0x6b0 fs/char_dev.c:417
   do_dentry_open+0x488/0x1160 fs/open.c:771
   vfs_open+0xa0/0xd0 fs/open.c:880
   do_last fs/namei.c:3416 [inline]
   path_openat+0x10e9/0x46e0 fs/namei.c:3533
   do_filp_open+0x1a1/0x280 fs/namei.c:3563
   do_sys_open+0x3fe/0x5d0 fs/open.c:1063
   __do_sys_openat fs/open.c:1090 [inline]
   __se_sys_openat fs/open.c:1084 [inline]
   __x64_sys_openat+0x9d/0x100 fs/open.c:1084
   do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
   entry_SYSCALL_64_after_hwframe+0x49/0xbe

  Freed by task 7789:
   save_stack+0x45/0xd0 mm/kasan/common.c:75
   set_track mm/kasan/common.c:87 [inline]
   __kasan_slab_free+0x102/0x150 mm/kasan/common.c:459
   kasan_slab_free+0xe/0x10 mm/kasan/common.c:467
   __cache_free mm/slab.c:3498 [inline]
   kfree+0xcf/0x230 mm/slab.c:3821
   alloc_workqueue+0xc3e/0xe70 kernel/workqueue.c:4295
   ucma_open+0x76/0x290 drivers/infiniband/core/ucma.c:1732
   misc_open+0x398/0x4c0 drivers/char/misc.c:141
   chrdev_open+0x247/0x6b0 fs/char_dev.c:417
   do_dentry_open+0x488/0x1160 fs/open.c:771
   vfs_open+0xa0/0xd0 fs/open.c:880
   do_last fs/namei.c:3416 [inline]
   path_openat+0x10e9/0x46e0 fs/namei.c:3533
   do_filp_open+0x1a1/0x280 fs/namei.c:3563
   do_sys_open+0x3fe/0x5d0 fs/open.c:1063
   __do_sys_openat fs/open.c:1090 [inline]
   __se_sys_openat fs/open.c:1084 [inline]
   __x64_sys_openat+0x9d/0x100 fs/open.c:1084
   do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
   entry_SYSCALL_64_after_hwframe+0x49/0xbe

  The buggy address belongs to the object at ffff888090fc2580
   which belongs to the cache kmalloc-512 of size 512
  The buggy address is located 280 bytes inside of
   512-byte region [ffff888090fc2580, ffff888090fc2780)

Reported-by: syzbot+17335689e239ce135d8b@syzkaller.appspotmail.com
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Fixes: 669de8bd ("kernel/workqueue: Use dynamic lockdep keys for workqueues")
Link: https://lkml.kernel.org/r/20190303220046.29448-1-bvanassche@acm.orgSigned-off-by: Ingo Molnar <mingo@kernel.org>

kernel/workqueue.c

@@ -4194,6 +4194,8 @@ struct workqueue_struct *alloc_workqueue(const char *fmt,
 	return wq;
 
 err_free_wq:
+	wq_unregister_lockdep(wq);
+	wq_free_lockdep(wq);
 	free_workqueue_attrs(wq->unbound_attrs);
 	kfree(wq);
 	return NULL;