Re: KASAN: use-after-free Read in btrfs_scan_one_device

[Johannes Thumshirn]

On 21/09/2020 07:38, syzbot wrote:
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    325d0eab Merge branch 'akpm' (patches from Andrew)
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1512df53900000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=6a8a2ae52ed737db
> dashboard link: https://syzkaller.appspot.com/bug?extid=582e66e5edf36a22c7b0
> compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12366f8b900000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14e6929b900000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+582e66e5edf36a22c7b0@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> ==================================================================
> BUG: KASAN: use-after-free in btrfs_printk+0x3eb/0x435 fs/btrfs/super.c:245
> Read of size 8 at addr ffff8880878e06a8 by task syz-executor225/7068
> 
> CPU: 1 PID: 7068 Comm: syz-executor225 Not tainted 5.9.0-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:77 [inline]
>  dump_stack+0x1d6/0x29e lib/dump_stack.c:118
>  print_address_description+0x66/0x620 mm/kasan/report.c:383
>  __kasan_report mm/kasan/report.c:513 [inline]
>  kasan_report+0x132/0x1d0 mm/kasan/report.c:530
>  btrfs_printk+0x3eb/0x435 fs/btrfs/super.c:245
>  device_list_add+0x1a88/0x1d60 fs/btrfs/volumes.c:943
>  btrfs_scan_one_device+0x196/0x490 fs/btrfs/volumes.c:1359
>  btrfs_mount_root+0x48f/0xb60 fs/btrfs/super.c:1634
>  legacy_get_tree+0xea/0x180 fs/fs_context.c:592
>  vfs_get_tree+0x88/0x270 fs/super.c:1547
>  fc_mount fs/namespace.c:978 [inline]
>  vfs_kern_mount+0xc9/0x160 fs/namespace.c:1008
>  btrfs_mount+0x33c/0xae0 fs/btrfs/super.c:1732
>  legacy_get_tree+0xea/0x180 fs/fs_context.c:592
>  vfs_get_tree+0x88/0x270 fs/super.c:1547
>  do_new_mount fs/namespace.c:2875 [inline]
>  path_mount+0x179d/0x29e0 fs/namespace.c:3192
>  do_mount fs/namespace.c:3205 [inline]
>  __do_sys_mount fs/namespace.c:3413 [inline]
>  __se_sys_mount+0x126/0x180 fs/namespace.c:3390
>  do_syscall_64+0x31/0x70 arch/x86/entry/common.c:46
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x44840a
> Code: b8 08 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 cd a2 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 0f 83 aa a2 fb ff c3 66 0f 1f 84 00 00 00 00 00
> RSP: 002b:00007ffedfffd608 EFLAGS: 00000293 ORIG_RAX: 00000000000000a5
> RAX: ffffffffffffffda RBX: 00007ffedfffd670 RCX: 000000000044840a
> RDX: 0000000020000000 RSI: 0000000020000100 RDI: 00007ffedfffd630
> RBP: 00007ffedfffd630 R08: 00007ffedfffd670 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000293 R12: 000000000000001a
> R13: 0000000000000004 R14: 0000000000000003 R15: 0000000000000003
> 
> Allocated by task 6945:
>  kasan_save_stack mm/kasan/common.c:48 [inline]
>  kasan_set_track mm/kasan/common.c:56 [inline]
>  __kasan_kmalloc+0x100/0x130 mm/kasan/common.c:461
>  kmalloc_node include/linux/slab.h:577 [inline]
>  kvmalloc_node+0x81/0x110 mm/util.c:574
>  kvmalloc include/linux/mm.h:757 [inline]
>  kvzalloc include/linux/mm.h:765 [inline]
>  btrfs_mount_root+0xd0/0xb60 fs/btrfs/super.c:1613
>  legacy_get_tree+0xea/0x180 fs/fs_context.c:592
>  vfs_get_tree+0x88/0x270 fs/super.c:1547
>  fc_mount fs/namespace.c:978 [inline]
>  vfs_kern_mount+0xc9/0x160 fs/namespace.c:1008
>  btrfs_mount+0x33c/0xae0 fs/btrfs/super.c:1732
>  legacy_get_tree+0xea/0x180 fs/fs_context.c:592
>  vfs_get_tree+0x88/0x270 fs/super.c:1547
>  do_new_mount fs/namespace.c:2875 [inline]
>  path_mount+0x179d/0x29e0 fs/namespace.c:3192
>  do_mount fs/namespace.c:3205 [inline]
>  __do_sys_mount fs/namespace.c:3413 [inline]
>  __se_sys_mount+0x126/0x180 fs/namespace.c:3390
>  do_syscall_64+0x31/0x70 arch/x86/entry/common.c:46
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> Freed by task 6945:
>  kasan_save_stack mm/kasan/common.c:48 [inline]
>  kasan_set_track+0x3d/0x70 mm/kasan/common.c:56
>  kasan_set_free_info+0x17/0x30 mm/kasan/generic.c:355
>  __kasan_slab_free+0xdd/0x110 mm/kasan/common.c:422
>  __cache_free mm/slab.c:3418 [inline]
>  kfree+0x113/0x200 mm/slab.c:3756
>  deactivate_locked_super+0xa7/0xf0 fs/super.c:335
>  btrfs_mount_root+0x72b/0xb60 fs/btrfs/super.c:1678
>  legacy_get_tree+0xea/0x180 fs/fs_context.c:592
>  vfs_get_tree+0x88/0x270 fs/super.c:1547
>  fc_mount fs/namespace.c:978 [inline]
>  vfs_kern_mount+0xc9/0x160 fs/namespace.c:1008
>  btrfs_mount+0x33c/0xae0 fs/btrfs/super.c:1732
>  legacy_get_tree+0xea/0x180 fs/fs_context.c:592
>  vfs_get_tree+0x88/0x270 fs/super.c:1547
>  do_new_mount fs/namespace.c:2875 [inline]
>  path_mount+0x179d/0x29e0 fs/namespace.c:3192
>  do_mount fs/namespace.c:3205 [inline]
>  __do_sys_mount fs/namespace.c:3413 [inline]
>  __se_sys_mount+0x126/0x180 fs/namespace.c:3390
>  do_syscall_64+0x31/0x70 arch/x86/entry/common.c:46
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> The buggy address belongs to the object at ffff8880878e0000
>  which belongs to the cache kmalloc-16k of size 16384
> The buggy address is located 1704 bytes inside of
>  16384-byte region [ffff8880878e0000, ffff8880878e4000)
> The buggy address belongs to the page:
> page:0000000060704f30 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x878e0
> head:0000000060704f30 order:3 compound_mapcount:0 compound_pincount:0
> flags: 0xfffe0000010200(slab|head)
> raw: 00fffe0000010200 ffffea00028e9a08 ffffea00021e3608 ffff8880aa440b00
> raw: 0000000000000000 ffff8880878e0000 0000000100000001 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>  ffff8880878e0580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8880878e0600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>> ffff8880878e0680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                   ^
>  ffff8880878e0700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8880878e0780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
> 
> 

Could reporoduce this one, working on it