Re: [moderation/CI] Re: block/fops: fix refcount underflow in __blkdev_direct_IO()

#syz upstream

On Wed, Jun 3, 2026 at 8:23 AM syzbot ci
<[email protected]> wrote:
>
> syzbot ci has tested the following series
>
> [v1] block/fops: fix refcount underflow in __blkdev_direct_IO()
> https://lore.kernel.org/all/[email protected]
> * [PATCH] block/fops: fix refcount underflow in __blkdev_direct_IO()
>
> and found the following issue:
> KASAN: invalid-free in mempool_free
>
> Full report is available here:
> https://ci.syzbot.org/series/3498c893-003a-4780-92e5-c3090ee3fe45
>
> ***
>
> KASAN: invalid-free in mempool_free
>
> tree:      torvalds
> URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/torvalds/linux
> base:      ba3e43a9e601636f5edb54e259a74f96ca3b8fd8
> arch:      amd64
> compiler:  Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
> config:    https://ci.syzbot.org/builds/0616259e-7b19-4982-aeee-0a50317c4cc6/config
> syz repro: https://ci.syzbot.org/findings/d2d98b4c-c6a9-4ecb-b313-ebd5a6d1b0d8/syz_repro
>
> ==================================================================
> BUG: KASAN: double-free in mempool_free+0xec/0x130 mm/mempool.c:711
> Free of addr ffff888177994400 by task syz.0.17/5875
>
> CPU: 1 UID: 0 PID: 5875 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
>  print_address_description+0x55/0x1e0 mm/kasan/report.c:378
>  print_report+0x58/0x70 mm/kasan/report.c:482
>  kasan_report_invalid_free+0xea/0x110 mm/kasan/report.c:557
>  check_slab_allocation mm/kasan/common.c:-1 [inline]
>  __kasan_slab_pre_free+0x104/0x120 mm/kasan/common.c:261
>  kasan_slab_pre_free include/linux/kasan.h:199 [inline]
>  slab_free_hook mm/slub.c:2634 [inline]
>  slab_free mm/slub.c:6251 [inline]
>  kmem_cache_free+0x130/0x650 mm/slub.c:6378
>  mempool_free+0xec/0x130 mm/mempool.c:711
>  bio_free+0x1e9/0x330 block/bio.c:205
>  __blkdev_direct_IO+0xd89/0xf40 block/fops.c:290
>  blkdev_direct_IO+0x121a/0x1790 block/fops.c:438
>  blkdev_read_iter+0x23d/0x440 block/fops.c:841
>  do_iter_readv_writev+0x619/0x8c0 fs/read_write.c:-1
>  vfs_readv+0x288/0x840 fs/read_write.c:1020
>  do_preadv fs/read_write.c:1134 [inline]
>  __do_sys_preadv2 fs/read_write.c:1193 [inline]
>  __se_sys_preadv2+0x184/0x2a0 fs/read_write.c:1184
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f125c99ce59
> Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 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 e8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007f125d829028 EFLAGS: 00000246 ORIG_RAX: 0000000000000147
> RAX: ffffffffffffffda RBX: 00007f125cc15fa0 RCX: 00007f125c99ce59
> RDX: 0000000000000005 RSI: 0000200000000080 RDI: 0000000000000003
> RBP: 00007f125ca32d6f R08: 0000000000000000 R09: 000000000000001f
> R10: 0000000000002000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007f125cc16038 R14: 00007f125cc15fa0 R15: 00007fff02d2e3e8
>  </TASK>
>
> Allocated by task 5875:
>  kasan_save_stack mm/kasan/common.c:57 [inline]
>  kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
>  unpoison_slab_object mm/kasan/common.c:340 [inline]
>  __kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:366
>  kasan_slab_alloc include/linux/kasan.h:253 [inline]
>  slab_post_alloc_hook mm/slub.c:4570 [inline]
>  slab_alloc_node mm/slub.c:4899 [inline]
>  kmem_cache_alloc_noprof+0x2bc/0x650 mm/slub.c:4906
>  bio_alloc_bioset+0x599/0xc90 block/bio.c:571
>  __blkdev_direct_IO+0x294/0xf40 block/fops.c:186
>  blkdev_direct_IO+0x121a/0x1790 block/fops.c:438
>  blkdev_read_iter+0x23d/0x440 block/fops.c:841
>  do_iter_readv_writev+0x619/0x8c0 fs/read_write.c:-1
>  vfs_readv+0x288/0x840 fs/read_write.c:1020
>  do_preadv fs/read_write.c:1134 [inline]
>  __do_sys_preadv2 fs/read_write.c:1193 [inline]
>  __se_sys_preadv2+0x184/0x2a0 fs/read_write.c:1184
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> Freed by task 5875:
>  kasan_save_stack mm/kasan/common.c:57 [inline]
>  kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
>  kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
>  poison_slab_object mm/kasan/common.c:253 [inline]
>  __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
>  kasan_slab_free include/linux/kasan.h:235 [inline]
>  slab_free_hook mm/slub.c:2689 [inline]
>  slab_free mm/slub.c:6251 [inline]
>  kmem_cache_free+0x182/0x650 mm/slub.c:6378
>  mempool_free+0xec/0x130 mm/mempool.c:711
>  bio_free+0x1e9/0x330 block/bio.c:205
>  __blkdev_direct_IO+0xd6e/0xf40 block/fops.c:288
>  blkdev_direct_IO+0x121a/0x1790 block/fops.c:438
>  blkdev_read_iter+0x23d/0x440 block/fops.c:841
>  do_iter_readv_writev+0x619/0x8c0 fs/read_write.c:-1
>  vfs_readv+0x288/0x840 fs/read_write.c:1020
>  do_preadv fs/read_write.c:1134 [inline]
>  __do_sys_preadv2 fs/read_write.c:1193 [inline]
>  __se_sys_preadv2+0x184/0x2a0 fs/read_write.c:1184
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> The buggy address belongs to the object at ffff888177994400
>  which belongs to the cache biovec-max of size 4096
> The buggy address is located 0 bytes inside of
>  4096-byte region [ffff888177994400, ffff888177995400)
>
> The buggy address belongs to the physical page:
> page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff888177990000 pfn:0x177990
> head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
> flags: 0x57ff00000000240(workingset|head|node=1|zone=2|lastcpupid=0x7ff)
> page_type: f5(slab)
> raw: 057ff00000000240 ffff8881604148c0 ffff8881622adc48 ffffea0005de5010
> raw: ffff888177990000 0000000800070003 00000000f5000000 0000000000000000
> head: 057ff00000000240 ffff8881604148c0 ffff8881622adc48 ffffea0005de5010
> head: ffff888177990000 0000000800070003 00000000f5000000 0000000000000000
> head: 057ff00000000003 fffffffffffffe01 00000000ffffffff 00000000ffffffff
> head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
> page dumped because: kasan: bad access detected
> page_owner tracks the page as allocated
> page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd2800(GFP_NOWAIT|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5065, tgid 5065 (udevd), ts 29098398773, free_ts 24434603765
>  set_page_owner include/linux/page_owner.h:32 [inline]
>  post_alloc_hook+0x22d/0x280 mm/page_alloc.c:1853
>  prep_new_page mm/page_alloc.c:1861 [inline]
>  get_page_from_freelist+0x2593/0x2610 mm/page_alloc.c:3941
>  __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5221
>  alloc_slab_page mm/slub.c:3278 [inline]
>  allocate_slab+0x77/0x660 mm/slub.c:3467
>  new_slab mm/slub.c:3525 [inline]
>  refill_objects+0x339/0x3d0 mm/slub.c:7272
>  refill_sheaf mm/slub.c:2816 [inline]
>  __pcs_replace_empty_main+0x321/0x720 mm/slub.c:4652
>  alloc_from_pcs mm/slub.c:4750 [inline]
>  slab_alloc_node mm/slub.c:4884 [inline]
>  kmem_cache_alloc_noprof+0x37d/0x650 mm/slub.c:4906
>  bio_alloc_bioset+0x599/0xc90 block/bio.c:571
>  bio_alloc include/linux/bio.h:367 [inline]
>  ext4_mpage_readpages+0x13b5/0x1f30 fs/ext4/readpage.c:355
>  read_pages+0x193/0x5a0 mm/readahead.c:163
>  page_cache_ra_unbounded+0x794/0xa10 mm/readahead.c:304
>  do_page_cache_ra mm/readahead.c:334 [inline]
>  page_cache_ra_order+0xae4/0xe80 mm/readahead.c:538
>  filemap_readahead mm/filemap.c:2664 [inline]
>  filemap_get_pages+0x897/0x1ef0 mm/filemap.c:2710
>  filemap_read+0x447/0x1230 mm/filemap.c:2806
>  __kernel_read+0x504/0x9b0 fs/read_write.c:532
>  integrity_kernel_read+0x89/0xd0 security/integrity/iint.c:28
> page last free pid 10 tgid 10 stack trace:
>  reset_page_owner include/linux/page_owner.h:25 [inline]
>  __free_pages_prepare mm/page_alloc.c:1397 [inline]
>  __free_frozen_pages+0xc1c/0xd30 mm/page_alloc.c:2938
>  vfree+0x1d1/0x2f0 mm/vmalloc.c:3472
>  delayed_vfree_work+0x55/0x80 mm/vmalloc.c:3392
>  process_one_work kernel/workqueue.c:3314 [inline]
>  process_scheduled_works+0xb5d/0x1860 kernel/workqueue.c:3397
>  worker_thread+0xa53/0xfc0 kernel/workqueue.c:3478
>  kthread+0x389/0x470 kernel/kthread.c:436
>  ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
>
> Memory state around the buggy address:
>  ffff888177994300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff888177994380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> >ffff888177994400: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                    ^
>  ffff888177994480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff888177994500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
>
>
> ***
>
> If these findings have caused you to resend the series or submit a
> separate fix, please add the following tag to your commit message:
>   Tested-by: [email protected]
>
> ---
> This report is generated by a bot. It may contain errors.
> syzbot ci engineers can be reached at [email protected].
>
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