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

[Eric Dumazet]

On 2/22/21 9:25 AM, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    f40ddce8 Linux 5.11
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=179e8d22d00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=e53d04227c52a0df
> dashboard link: https://syzkaller.appspot.com/bug?extid=429d3f82d757c211bff3
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10d190cad00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13dc8a82d00000
> 
> Bisection is inconclusive: the issue happens on the oldest tested release.
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1128ae60d00000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=1328ae60d00000
> console output: https://syzkaller.appspot.com/x/log.txt?x=1528ae60d00000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+429d3f82d757c211bff3@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> ==================================================================
> BUG: KASAN: use-after-free in instrument_atomic_read include/linux/instrumented.h:71 [inline]
> BUG: KASAN: use-after-free in atomic_read include/asm-generic/atomic-instrumented.h:27 [inline]
> BUG: KASAN: use-after-free in refcount_dec_not_one+0x71/0x1e0 lib/refcount.c:76
> Read of size 4 at addr ffff888014ca19a0 by task syz-executor980/8540
> 
> CPU: 0 PID: 8540 Comm: syz-executor980 Not tainted 5.11.0-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+0x107/0x163 lib/dump_stack.c:120
>  print_address_description.constprop.0.cold+0x5b/0x2f8 mm/kasan/report.c:230
>  __kasan_report mm/kasan/report.c:396 [inline]
>  kasan_report.cold+0x79/0xd5 mm/kasan/report.c:413
>  check_memory_region_inline mm/kasan/generic.c:179 [inline]
>  check_memory_region+0x13d/0x180 mm/kasan/generic.c:185
>  instrument_atomic_read include/linux/instrumented.h:71 [inline]
>  atomic_read include/asm-generic/atomic-instrumented.h:27 [inline]
>  refcount_dec_not_one+0x71/0x1e0 lib/refcount.c:76
>  refcount_dec_and_mutex_lock+0x19/0x140 lib/refcount.c:115
>  nbd_put drivers/block/nbd.c:248 [inline]
>  nbd_genl_connect+0xee7/0x1560 drivers/block/nbd.c:1980
>  genl_family_rcv_msg_doit+0x228/0x320 net/netlink/genetlink.c:739
>  genl_family_rcv_msg net/netlink/genetlink.c:783 [inline]
>  genl_rcv_msg+0x328/0x580 net/netlink/genetlink.c:800
>  netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2494
>  genl_rcv+0x24/0x40 net/netlink/genetlink.c:811
>  netlink_unicast_kernel net/netlink/af_netlink.c:1304 [inline]
>  netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1330
>  netlink_sendmsg+0x856/0xd90 net/netlink/af_netlink.c:1919
>  sock_sendmsg_nosec net/socket.c:652 [inline]
>  sock_sendmsg+0xcf/0x120 net/socket.c:672
>  ____sys_sendmsg+0x6e8/0x810 net/socket.c:2345
>  ___sys_sendmsg+0xf3/0x170 net/socket.c:2399
>  __sys_sendmsg+0xe5/0x1b0 net/socket.c:2432
>  do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x440709
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 e1 14 00 00 90 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 c0 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007ffd63e9cc88 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
> RAX: ffffffffffffffda RBX: 000000000000e3fb RCX: 0000000000440709
> RDX: 0000000000000000 RSI: 0000000020000340 RDI: 0000000000000003
> RBP: 0000000000000000 R08: 0000000000000000 R09: 00007ffd63e9ce28
> R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffd63e9cc9c
> R13: 431bde82d7b634db R14: 00000000004ae018 R15: 00000000004004a0
> 
> Allocated by task 8536:
>  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:401 [inline]
>  ____kasan_kmalloc.constprop.0+0x82/0xa0 mm/kasan/common.c:429
>  kmalloc include/linux/slab.h:552 [inline]
>  kzalloc include/linux/slab.h:682 [inline]
>  nbd_dev_add+0x44/0x8e0 drivers/block/nbd.c:1673
>  nbd_genl_connect+0x59c/0x1560 drivers/block/nbd.c:1838
>  genl_family_rcv_msg_doit+0x228/0x320 net/netlink/genetlink.c:739
>  genl_family_rcv_msg net/netlink/genetlink.c:783 [inline]
>  genl_rcv_msg+0x328/0x580 net/netlink/genetlink.c:800
>  netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2494
>  genl_rcv+0x24/0x40 net/netlink/genetlink.c:811
>  netlink_unicast_kernel net/netlink/af_netlink.c:1304 [inline]
>  netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1330
>  netlink_sendmsg+0x856/0xd90 net/netlink/af_netlink.c:1919
>  sock_sendmsg_nosec net/socket.c:652 [inline]
>  sock_sendmsg+0xcf/0x120 net/socket.c:672
>  ____sys_sendmsg+0x6e8/0x810 net/socket.c:2345
>  ___sys_sendmsg+0xf3/0x170 net/socket.c:2399
>  __sys_sendmsg+0xe5/0x1b0 net/socket.c:2432
>  do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> Freed by task 8540:
>  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:356
>  ____kasan_slab_free+0xe1/0x110 mm/kasan/common.c:362
>  kasan_slab_free include/linux/kasan.h:192 [inline]
>  slab_free_hook mm/slub.c:1547 [inline]
>  slab_free_freelist_hook+0x5d/0x150 mm/slub.c:1580
>  slab_free mm/slub.c:3143 [inline]
>  kfree+0xdb/0x3b0 mm/slub.c:4139
>  nbd_dev_remove drivers/block/nbd.c:243 [inline]
>  nbd_put.part.0+0x180/0x1d0 drivers/block/nbd.c:251
>  nbd_put drivers/block/nbd.c:295 [inline]
>  nbd_config_put+0x6dd/0x8c0 drivers/block/nbd.c:1242
>  nbd_genl_connect+0xeb7/0x1560 drivers/block/nbd.c:1978
>  genl_family_rcv_msg_doit+0x228/0x320 net/netlink/genetlink.c:739
>  genl_family_rcv_msg net/netlink/genetlink.c:783 [inline]
>  genl_rcv_msg+0x328/0x580 net/netlink/genetlink.c:800
>  netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2494
>  genl_rcv+0x24/0x40 net/netlink/genetlink.c:811
>  netlink_unicast_kernel net/netlink/af_netlink.c:1304 [inline]
>  netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1330
>  netlink_sendmsg+0x856/0xd90 net/netlink/af_netlink.c:1919
>  sock_sendmsg_nosec net/socket.c:652 [inline]
>  sock_sendmsg+0xcf/0x120 net/socket.c:672
>  ____sys_sendmsg+0x6e8/0x810 net/socket.c:2345
>  ___sys_sendmsg+0xf3/0x170 net/socket.c:2399
>  __sys_sendmsg+0xe5/0x1b0 net/socket.c:2432
>  do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> The buggy address belongs to the object at ffff888014ca1800
>  which belongs to the cache kmalloc-1k of size 1024
> The buggy address is located 416 bytes inside of
>  1024-byte region [ffff888014ca1800, ffff888014ca1c00)
> The buggy address belongs to the page:
> page:0000000086766889 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x14ca0
> head:0000000086766889 order:3 compound_mapcount:0 compound_pincount:0
> flags: 0xfff00000010200(slab|head)
> raw: 00fff00000010200 ffffea0000929400 0000000200000002 ffff888010c41140
> raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>  ffff888014ca1880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff888014ca1900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>> ffff888014ca1980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                ^
>  ffff888014ca1a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff888014ca1a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> syzbot can test patches for this issue, for details see:
> https://goo.gl/tpsmEJ#testing-patches
> 

This might be caused by :

commit a2c97909f97ef32b76e856572fba4f77e1885fe6
Author: Josef Bacik <josef@xxxxxxxxxxxxxx>
Date:   Thu Apr 6 17:02:07 2017 -0400

    nbd: add a flag to destroy an nbd device on disconnect
   
    For ease of management it would be nice for users to specify that the
    device node for a nbd device is destroyed once it is disconnected and
    there are no more users.  Add a client flag and enable this operation to
    happen.
   
    Signed-off-by: Josef Bacik <jbacik@xxxxxx>
    Signed-off-by: Jens Axboe <axboe@xxxxxx>