Re: [syzbot] KASAN: use-after-free Read in tctx_task_work (2)

[Pavel Begunkov]

On 8/19/21 11:44 AM, syzbot wrote:
> Hello,
> 
> syzbot has tested the proposed patch but the reproducer is still triggering an issue:
> KASAN: use-after-free Read in tctx_task_work
> 
> ==================================================================
> BUG: KASAN: use-after-free in ctx_flush_and_put fs/io_uring.c:2002 [inline]
> BUG: KASAN: use-after-free in tctx_task_work+0x307/0x310 fs/io_uring.c:2049
> Read of size 4 at addr ffff888029d66358 by task syz-executor530/27775

#syz test: https://github.com/isilence/linux.git syztest_ctx_tw

> 
> CPU: 0 PID: 27775 Comm: syz-executor530 Not tainted 5.14.0-rc5-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:88 [inline]
>  dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:105
>  print_address_description.constprop.0.cold+0x6c/0x309 mm/kasan/report.c:233
>  __kasan_report mm/kasan/report.c:419 [inline]
>  kasan_report.cold+0x83/0xdf mm/kasan/report.c:436
>  ctx_flush_and_put fs/io_uring.c:2002 [inline]
>  tctx_task_work+0x307/0x310 fs/io_uring.c:2049
>  task_work_run+0xdd/0x1a0 kernel/task_work.c:164
>  exit_task_work include/linux/task_work.h:32 [inline]
>  do_exit+0xbae/0x2a30 kernel/exit.c:825
>  do_group_exit+0x125/0x310 kernel/exit.c:922
>  get_signal+0x47f/0x2160 kernel/signal.c:2808
>  arch_do_signal_or_restart+0x2a9/0x1c40 arch/x86/kernel/signal.c:865
>  handle_signal_work kernel/entry/common.c:148 [inline]
>  exit_to_user_mode_loop kernel/entry/common.c:172 [inline]
>  exit_to_user_mode_prepare+0x17d/0x290 kernel/entry/common.c:209
>  __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
>  syscall_exit_to_user_mode+0x19/0x60 kernel/entry/common.c:302
>  do_syscall_64+0x42/0xb0 arch/x86/entry/common.c:86
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
> RIP: 0033:0x446729
> Code: Unable to access opcode bytes at RIP 0x4466ff.
> RSP: 002b:00007fada1a521e8 EFLAGS: 00000246 ORIG_RAX: 00000000000001aa
> RAX: 00000000000001d2 RBX: 00000000004cb458 RCX: 0000000000446729
> RDX: 0000000000000000 RSI: 0000000000006b46 RDI: 0000000000000006
> RBP: 00000000004cb450 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000004cb45c
> R13: 00007ffff39bb49f R14: 00007fada1a52300 R15: 0000000000022000
> 
> Allocated by task 27776:
>  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38
>  kasan_set_track mm/kasan/common.c:46 [inline]
>  set_alloc_info mm/kasan/common.c:434 [inline]
>  ____kasan_kmalloc mm/kasan/common.c:513 [inline]
>  ____kasan_kmalloc mm/kasan/common.c:472 [inline]
>  __kasan_kmalloc+0x9b/0xd0 mm/kasan/common.c:522
>  kmalloc include/linux/slab.h:591 [inline]
>  kzalloc include/linux/slab.h:721 [inline]
>  io_ring_ctx_alloc fs/io_uring.c:1206 [inline]
>  io_uring_create fs/io_uring.c:9685 [inline]
>  io_uring_setup+0x27d/0x2cf0 fs/io_uring.c:9791
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
> 
> Freed by task 10491:
>  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38
>  kasan_set_track+0x1c/0x30 mm/kasan/common.c:46
>  kasan_set_free_info+0x20/0x30 mm/kasan/generic.c:360
>  ____kasan_slab_free mm/kasan/common.c:366 [inline]
>  ____kasan_slab_free mm/kasan/common.c:328 [inline]
>  __kasan_slab_free+0xfb/0x130 mm/kasan/common.c:374
>  kasan_slab_free include/linux/kasan.h:230 [inline]
>  slab_free_hook mm/slub.c:1625 [inline]
>  slab_free_freelist_hook+0xdf/0x240 mm/slub.c:1650
>  slab_free mm/slub.c:3210 [inline]
>  kfree+0xe4/0x530 mm/slub.c:4264
>  io_ring_ctx_free fs/io_uring.c:8712 [inline]
>  io_ring_exit_work+0x13ba/0x1930 fs/io_uring.c:8861
>  process_one_work+0x98d/0x1630 kernel/workqueue.c:2276
>  worker_thread+0x658/0x11f0 kernel/workqueue.c:2422
>  kthread+0x3e5/0x4d0 kernel/kthread.c:319
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
> 
> Last potentially related work creation:
>  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38
>  kasan_record_aux_stack+0xe5/0x110 mm/kasan/generic.c:348
>  insert_work+0x48/0x370 kernel/workqueue.c:1332
>  __queue_work+0x5c1/0xed0 kernel/workqueue.c:1498
>  queue_work_on+0xee/0x110 kernel/workqueue.c:1525
>  queue_work include/linux/workqueue.h:507 [inline]
>  io_ring_ctx_wait_and_kill+0x30a/0x3c0 fs/io_uring.c:8914
>  io_uring_release+0x3e/0x50 fs/io_uring.c:8922
>  __fput+0x288/0x920 fs/file_table.c:280
>  task_work_run+0xdd/0x1a0 kernel/task_work.c:164
>  exit_task_work include/linux/task_work.h:32 [inline]
>  do_exit+0xbae/0x2a30 kernel/exit.c:825
>  do_group_exit+0x125/0x310 kernel/exit.c:922
>  get_signal+0x47f/0x2160 kernel/signal.c:2808
>  arch_do_signal_or_restart+0x2a9/0x1c40 arch/x86/kernel/signal.c:865
>  handle_signal_work kernel/entry/common.c:148 [inline]
>  exit_to_user_mode_loop kernel/entry/common.c:172 [inline]
>  exit_to_user_mode_prepare+0x17d/0x290 kernel/entry/common.c:209
>  __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
>  syscall_exit_to_user_mode+0x19/0x60 kernel/entry/common.c:302
>  do_syscall_64+0x42/0xb0 arch/x86/entry/common.c:86
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
> 
> Second to last potentially related work creation:
>  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38
>  kasan_record_aux_stack+0xe5/0x110 mm/kasan/generic.c:348
>  insert_work+0x48/0x370 kernel/workqueue.c:1332
>  __queue_work+0x5c1/0xed0 kernel/workqueue.c:1498
>  queue_work_on+0xee/0x110 kernel/workqueue.c:1525
>  queue_work include/linux/workqueue.h:507 [inline]
>  io_ring_ctx_wait_and_kill+0x30a/0x3c0 fs/io_uring.c:8914
>  io_uring_release+0x3e/0x50 fs/io_uring.c:8922
>  __fput+0x288/0x920 fs/file_table.c:280
>  task_work_run+0xdd/0x1a0 kernel/task_work.c:164
>  exit_task_work include/linux/task_work.h:32 [inline]
>  do_exit+0xbae/0x2a30 kernel/exit.c:825
>  do_group_exit+0x125/0x310 kernel/exit.c:922
>  get_signal+0x47f/0x2160 kernel/signal.c:2808
>  arch_do_signal_or_restart+0x2a9/0x1c40 arch/x86/kernel/signal.c:865
>  handle_signal_work kernel/entry/common.c:148 [inline]
>  exit_to_user_mode_loop kernel/entry/common.c:172 [inline]
>  exit_to_user_mode_prepare+0x17d/0x290 kernel/entry/common.c:209
>  __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
>  syscall_exit_to_user_mode+0x19/0x60 kernel/entry/common.c:302
>  do_syscall_64+0x42/0xb0 arch/x86/entry/common.c:86
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
> 
> The buggy address belongs to the object at ffff888029d66000
>  which belongs to the cache kmalloc-4k of size 4096
> The buggy address is located 856 bytes inside of
>  4096-byte region [ffff888029d66000, ffff888029d67000)
> The buggy address belongs to the page:
> page:ffffea0000a75800 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x29d60
> head:ffffea0000a75800 order:3 compound_mapcount:0 compound_pincount:0
> flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
> raw: 00fff00000010200 dead000000000100 dead000000000122 ffff888010842140
> raw: 0000000000000000 0000000000040004 00000001ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
> page_owner tracks the page as allocated
> page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd2040(__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 6467, ts 58396905717, free_ts 57689976074
>  prep_new_page mm/page_alloc.c:2436 [inline]
>  get_page_from_freelist+0xa72/0x2f80 mm/page_alloc.c:4169
>  __alloc_pages+0x1b2/0x500 mm/page_alloc.c:5391
>  alloc_pages+0x18c/0x2a0 mm/mempolicy.c:2244
>  alloc_slab_page mm/slub.c:1688 [inline]
>  allocate_slab+0x32e/0x4b0 mm/slub.c:1828
>  new_slab mm/slub.c:1891 [inline]
>  new_slab_objects mm/slub.c:2637 [inline]
>  ___slab_alloc+0x4ba/0x820 mm/slub.c:2800
>  __slab_alloc.constprop.0+0xa7/0xf0 mm/slub.c:2840
>  slab_alloc_node mm/slub.c:2922 [inline]
>  slab_alloc mm/slub.c:2964 [inline]
>  __kmalloc+0x312/0x330 mm/slub.c:4108
>  kmalloc include/linux/slab.h:596 [inline]
>  tomoyo_realpath_from_path+0xc3/0x620 security/tomoyo/realpath.c:254
>  tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
>  tomoyo_path_perm+0x21b/0x400 security/tomoyo/file.c:822
>  security_inode_getattr+0xcf/0x140 security/security.c:1332
>  vfs_getattr fs/stat.c:139 [inline]
>  vfs_statx+0x164/0x390 fs/stat.c:207
>  vfs_fstatat fs/stat.c:225 [inline]
>  vfs_lstat include/linux/fs.h:3386 [inline]
>  __do_sys_newlstat+0x91/0x110 fs/stat.c:380
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
> page last free stack trace:
>  reset_page_owner include/linux/page_owner.h:24 [inline]
>  free_pages_prepare mm/page_alloc.c:1346 [inline]
>  free_pcp_prepare+0x2c5/0x780 mm/page_alloc.c:1397
>  free_unref_page_prepare mm/page_alloc.c:3332 [inline]
>  free_unref_page+0x19/0x690 mm/page_alloc.c:3411
>  qlink_free mm/kasan/quarantine.c:146 [inline]
>  qlist_free_all+0x5a/0xc0 mm/kasan/quarantine.c:165
>  kasan_quarantine_reduce+0x180/0x200 mm/kasan/quarantine.c:272
>  __kasan_slab_alloc+0x8e/0xa0 mm/kasan/common.c:444
>  kasan_slab_alloc include/linux/kasan.h:254 [inline]
>  slab_post_alloc_hook mm/slab.h:519 [inline]
>  slab_alloc_node mm/slub.c:2956 [inline]
>  slab_alloc mm/slub.c:2964 [inline]
>  kmem_cache_alloc+0x285/0x4a0 mm/slub.c:2969
>  getname_flags.part.0+0x50/0x4f0 fs/namei.c:138
>  getname_flags include/linux/audit.h:319 [inline]
>  getname+0x8e/0xd0 fs/namei.c:209
>  do_sys_openat2+0xf5/0x420 fs/open.c:1198
>  do_sys_open fs/open.c:1220 [inline]
>  __do_sys_open fs/open.c:1228 [inline]
>  __se_sys_open fs/open.c:1224 [inline]
>  __x64_sys_open+0x119/0x1c0 fs/open.c:1224
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
> 
> Memory state around the buggy address:
>  ffff888029d66200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff888029d66280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>> ffff888029d66300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                                     ^
>  ffff888029d66380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff888029d66400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
> 
> 
> Tested on:
> 
> commit:         bdd748b6 io-wq: move nr_running and worker_refs out of..
> git tree:       git://git.kernel.dk/linux-block for-5.15/io_uring
> console output: https://syzkaller.appspot.com/x/log.txt?x=13141b61300000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=cb4282936412304f
> dashboard link: https://syzkaller.appspot.com/bug?extid=9c3492b27d10dc49ffa6
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.1
> 

-- 
Pavel Begunkov