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Date:   Sun, 21 Mar 2021 14:39:09 -0700
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Subject: Re: [syzbot] KASAN: use-after-free Read in disk_part_iter_next (2)
From:   syzbot <syzbot+8fede7e30c7cee0de139@syzkaller.appspotmail.com>
To:     axboe@kernel.dk, bvanassche@acm.org, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com
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Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KASAN: use-after-free Read in disk_part_iter_next

==================================================================
BUG: KASAN: use-after-free in bdev_nr_sectors include/linux/genhd.h:266 [inline]
BUG: KASAN: use-after-free in disk_part_iter_next+0x49d/0x530 block/genhd.c:206
Read of size 8 at addr ffff88801626b9a8 by task syz-executor.0/10146

CPU: 0 PID: 10146 Comm: syz-executor.0 Not tainted 5.12.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack+0x141/0x1d7 lib/dump_stack.c:120
 print_address_description.constprop.0.cold+0x5b/0x2f8 mm/kasan/report.c:232
 __kasan_report mm/kasan/report.c:399 [inline]
 kasan_report.cold+0x7c/0xd8 mm/kasan/report.c:416
 bdev_nr_sectors include/linux/genhd.h:266 [inline]
 disk_part_iter_next+0x49d/0x530 block/genhd.c:206
 blk_drop_partitions+0x10a/0x180 block/partitions/core.c:543
 bdev_disk_changed+0x238/0x430 fs/block_dev.c:1246
 __loop_clr_fd+0x7c7/0xff0 drivers/block/loop.c:1271
 lo_release+0x1ac/0x1f0 drivers/block/loop.c:1923
 __blkdev_put+0x54e/0x800 fs/block_dev.c:1588
 blkdev_put+0x92/0x580 fs/block_dev.c:1641
 blkdev_close+0x8c/0xb0 fs/block_dev.c:1649
 __fput+0x288/0x920 fs/file_table.c:280
 task_work_run+0xdd/0x1a0 kernel/task_work.c:140
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:174 [inline]
 exit_to_user_mode_prepare+0x249/0x250 kernel/entry/common.c:208
 __syscall_exit_to_user_mode_work kernel/entry/common.c:290 [inline]
 syscall_exit_to_user_mode+0x19/0x60 kernel/entry/common.c:301
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x41926b
Code: 0f 05 48 3d 00 f0 ff ff 77 45 c3 0f 1f 40 00 48 83 ec 18 89 7c 24 0c e8 63 fc ff ff 8b 7c 24 0c 41 89 c0 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 35 44 89 c7 89 44 24 0c e8 a1 fc ff ff 8b 44
RSP: 002b:00007ffc4fc09520 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000004 RCX: 000000000041926b
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000003
RBP: 0000000000000001 R08: 0000000000000000 R09: 0000001b30620070
R10: 0000000000000000 R11: 0000000000000293 R12: 000000000056c9e0
R13: 000000000056c9e0 R14: 000000000056bf60 R15: 0000000000013222

Allocated by task 10160:
 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:427 [inline]
 __kasan_slab_alloc+0x75/0x90 mm/kasan/common.c:460
 kasan_slab_alloc include/linux/kasan.h:223 [inline]
 slab_post_alloc_hook mm/slab.h:516 [inline]
 slab_alloc_node mm/slub.c:2907 [inline]
 slab_alloc mm/slub.c:2915 [inline]
 kmem_cache_alloc+0x155/0x370 mm/slub.c:2920
 bdev_alloc_inode+0x18/0x80 fs/block_dev.c:795
 alloc_inode+0x61/0x230 fs/inode.c:234
 new_inode_pseudo fs/inode.c:928 [inline]
 new_inode+0x27/0x2f0 fs/inode.c:957
 bdev_alloc+0x20/0x2f0 fs/block_dev.c:885
 add_partition+0x1ab/0x880 block/partitions/core.c:348
 bdev_add_partition+0xb6/0x130 block/partitions/core.c:451
 blkpg_do_ioctl+0x2d0/0x340 block/ioctl.c:43
 blkpg_ioctl block/ioctl.c:60 [inline]
 blkdev_ioctl+0x577/0x6d0 block/ioctl.c:548
 block_ioctl+0xf9/0x140 fs/block_dev.c:1667
 vfs_ioctl fs/ioctl.c:48 [inline]
 __do_sys_ioctl fs/ioctl.c:753 [inline]
 __se_sys_ioctl fs/ioctl.c:739 [inline]
 __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:739
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Freed by task 13:
 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:357
 ____kasan_slab_free mm/kasan/common.c:360 [inline]
 ____kasan_slab_free mm/kasan/common.c:325 [inline]
 __kasan_slab_free+0xf5/0x130 mm/kasan/common.c:367
 kasan_slab_free include/linux/kasan.h:199 [inline]
 slab_free_hook mm/slub.c:1562 [inline]
 slab_free_freelist_hook+0x92/0x210 mm/slub.c:1600
 slab_free mm/slub.c:3161 [inline]
 kmem_cache_free+0x8a/0x740 mm/slub.c:3177
 i_callback+0x3f/0x70 fs/inode.c:223
 rcu_do_batch kernel/rcu/tree.c:2559 [inline]
 rcu_core+0x74a/0x12f0 kernel/rcu/tree.c:2794
 __do_softirq+0x29b/0x9f6 kernel/softirq.c:345

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:345
 __call_rcu kernel/rcu/tree.c:3039 [inline]
 call_rcu+0xb1/0x740 kernel/rcu/tree.c:3114
 destroy_inode+0x129/0x1b0 fs/inode.c:289
 iput_final fs/inode.c:1654 [inline]
 iput.part.0+0x57e/0x810 fs/inode.c:1680
 iput+0x58/0x70 fs/inode.c:1670
 disk_part_iter_exit block/genhd.c:235 [inline]
 disk_part_iter_next+0x9a/0x530 block/genhd.c:202
 blk_drop_partitions+0x10a/0x180 block/partitions/core.c:543
 bdev_disk_changed+0x238/0x430 fs/block_dev.c:1246
 loop_reread_partitions+0x29/0x50 drivers/block/loop.c:655
 loop_set_status+0x704/0x1050 drivers/block/loop.c:1418
 loop_set_status64 drivers/block/loop.c:1538 [inline]
 lo_ioctl+0x4ca/0x1620 drivers/block/loop.c:1706
 blkdev_ioctl+0x2a1/0x6d0 block/ioctl.c:583
 block_ioctl+0xf9/0x140 fs/block_dev.c:1667
 vfs_ioctl fs/ioctl.c:48 [inline]
 __do_sys_ioctl fs/ioctl.c:753 [inline]
 __se_sys_ioctl fs/ioctl.c:739 [inline]
 __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:739
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

The buggy address belongs to the object at ffff88801626b980
 which belongs to the cache bdev_cache of size 2792
The buggy address is located 40 bytes inside of
 2792-byte region [ffff88801626b980, ffff88801626c468)
The buggy address belongs to the page:
page:ffffea0000589a00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x16268
head:ffffea0000589a00 order:3 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head)
raw: 00fff00000010200 dead000000000100 dead000000000122 ffff8880101bdb40
raw: 0000000000000000 00000000800b000b 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88801626b880: 00 00 00 00 00 00 00 00 00 00 00 00 00 fc fc fc
 ffff88801626b900: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88801626b980: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                  ^
 ffff88801626ba00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88801626ba80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


Tested on:

commit:         a5f35387 block: Fix a race between reading and freeing par..
git tree:       https://github.com/bvanassche/linux
console output: https://syzkaller.appspot.com/x/log.txt?x=13534e62d00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=b5da36c3359b30d1
dashboard link: https://syzkaller.appspot.com/bug?extid=8fede7e30c7cee0de139
compiler: