linux-stable.git/drivers/block/nbd.c, branch linux-5.15.y

nbd: defer config unlock in nbd_genl_connect

2026-01-19T12:09:28+00:00

[ Upstream commit 1649714b930f9ea6233ce0810ba885999da3b5d4 ]

There is one use-after-free warning when running NBD_CMD_CONNECT and
NBD_CLEAR_SOCK:

nbd_genl_connect
  nbd_alloc_and_init_config // config_refs=1
  nbd_start_device // config_refs=2
  set NBD_RT_HAS_CONFIG_REF			open nbd // config_refs=3
  recv_work done // config_refs=2
						NBD_CLEAR_SOCK // config_refs=1
						close nbd // config_refs=0
  refcount_inc -> uaf

------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 24 PID: 1014 at lib/refcount.c:25 refcount_warn_saturate+0x12e/0x290
 nbd_genl_connect+0x16d0/0x1ab0
 genl_family_rcv_msg_doit+0x1f3/0x310
 genl_rcv_msg+0x44a/0x790

The issue can be easily reproduced by adding a small delay before
refcount_inc(&nbd->config_refs) in nbd_genl_connect():

        mutex_unlock(&nbd->config_lock);
        if (!ret) {
                set_bit(NBD_RT_HAS_CONFIG_REF, &config->runtime_flags);
+               printk("before sleep\n");
+               mdelay(5 * 1000);
+               printk("after sleep\n");
                refcount_inc(&nbd->config_refs);
                nbd_connect_reply(info, nbd->index);
        }

Fixes: e46c7287b1c2 ("nbd: add a basic netlink interface")
Signed-off-by: Zheng Qixing 
Reviewed-by: Yu Kuai 
Signed-off-by: Jens Axboe 
Signed-off-by: Sasha Levin

nbd: defer config put in recv_work

2026-01-19T12:09:27+00:00

[ Upstream commit 9517b82d8d422d426a988b213fdd45c6b417b86d ]

There is one uaf issue in recv_work when running NBD_CLEAR_SOCK and
NBD_CMD_RECONFIGURE:
  nbd_genl_connect     // conf_ref=2 (connect and recv_work A)
  nbd_open	       // conf_ref=3
  recv_work A done     // conf_ref=2
  NBD_CLEAR_SOCK       // conf_ref=1
  nbd_genl_reconfigure // conf_ref=2 (trigger recv_work B)
  close nbd	       // conf_ref=1
  recv_work B
    config_put         // conf_ref=0
    atomic_dec(&config->recv_threads); -> UAF

Or only running NBD_CLEAR_SOCK:
  nbd_genl_connect   // conf_ref=2
  nbd_open 	     // conf_ref=3
  NBD_CLEAR_SOCK     // conf_ref=2
  close nbd
    nbd_release
      config_put     // conf_ref=1
  recv_work
    config_put 	     // conf_ref=0
    atomic_dec(&config->recv_threads); -> UAF

Commit 87aac3a80af5 ("nbd: call nbd_config_put() before notifying the
waiter") moved nbd_config_put() to run before waking up the waiter in
recv_work, in order to ensure that nbd_start_device_ioctl() would not
be woken up while nbd->task_recv was still uncleared.

However, in nbd_start_device_ioctl(), after being woken up it explicitly
calls flush_workqueue() to make sure all current works are finished.
Therefore, there is no need to move the config put ahead of the wakeup.

Move nbd_config_put() to the end of recv_work, so that the reference is
held for the whole lifetime of the worker thread. This makes sure the
config cannot be freed while recv_work is still running, even if clear
+ reconfigure interleave.

In addition, we don't need to worry about recv_work dropping the last
nbd_put (which causes deadlock):

path A (netlink with NBD_CFLAG_DESTROY_ON_DISCONNECT):
  connect  // nbd_refs=1 (trigger recv_work)
  open nbd // nbd_refs=2
  NBD_CLEAR_SOCK
  close nbd
    nbd_release
      nbd_disconnect_and_put
        flush_workqueue // recv_work done
      nbd_config_put
        nbd_put // nbd_refs=1
      nbd_put // nbd_refs=0
        queue_work

path B (netlink without NBD_CFLAG_DESTROY_ON_DISCONNECT):
  connect  // nbd_refs=2 (trigger recv_work)
  open nbd // nbd_refs=3
  NBD_CLEAR_SOCK // conf_refs=2
  close nbd
    nbd_release
      nbd_config_put // conf_refs=1
      nbd_put // nbd_refs=2
  recv_work done // conf_refs=0, nbd_refs=1
  rmmod // nbd_refs=0

Reported-by: syzbot+56fbf4c7ddf65e95c7cc@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/6907edce.a70a0220.37351b.0014.GAE@google.com/T/
Fixes: 87aac3a80af5 ("nbd: make the config put is called before the notifying the waiter")
Depends-on: e2daec488c57 ("nbd: Fix hungtask when nbd_config_put")
Signed-off-by: Zheng Qixing 
Signed-off-by: Jens Axboe 
Signed-off-by: Sasha Levin

nbd: partition nbd_read_stat() into nbd_read_reply() and nbd_handle_reply()

2026-01-19T12:09:27+00:00

[ Upstream commit 3fe1db626a56cdf259c348404f2c5429e2f065a1 ]

Prepare to fix uaf in nbd_read_stat(), no functional changes.

Signed-off-by: Yu Kuai 
Reviewed-by: Ming Lei 
Reviewed-by: Josef Bacik 
Link: https://lore.kernel.org/r/20210916093350.1410403-7-yukuai3@huawei.com
Signed-off-by: Jens Axboe 
Stable-dep-of: 9517b82d8d42 ("nbd: defer config put in recv_work")
Signed-off-by: Sasha Levin

nbd: clean up return value checking of sock_xmit()

2026-01-19T12:09:27+00:00

[ Upstream commit f52c0e08237e7864a44311fc78bc9bf2e045611b ]

Check if sock_xmit() return 0 is useless because it'll never return
0, comment it and remove such checkings.

Signed-off-by: Yu Kuai 
Reviewed-by: Ming Lei 
Reviewed-by: Josef Bacik 
Link: https://lore.kernel.org/r/20210916093350.1410403-6-yukuai3@huawei.com
Signed-off-by: Jens Axboe 
Stable-dep-of: 9517b82d8d42 ("nbd: defer config put in recv_work")
Signed-off-by: Sasha Levin

nbd: fix uaf in nbd_genl_connect() error path

2025-07-17T16:30:52+00:00

[ Upstream commit aa9552438ebf015fc5f9f890dbfe39f0c53cf37e ]

There is a use-after-free issue in nbd:

block nbd6: Receive control failed (result -104)
block nbd6: shutting down sockets
==================================================================
BUG: KASAN: slab-use-after-free in recv_work+0x694/0xa80 drivers/block/nbd.c:1022
Write of size 4 at addr ffff8880295de478 by task kworker/u33:0/67

CPU: 2 UID: 0 PID: 67 Comm: kworker/u33:0 Not tainted 6.15.0-rc5-syzkaller-00123-g2c89c1b655c0 #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Workqueue: nbd6-recv recv_work
Call Trace:
 
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:408 [inline]
 print_report+0xc3/0x670 mm/kasan/report.c:521
 kasan_report+0xe0/0x110 mm/kasan/report.c:634
 check_region_inline mm/kasan/generic.c:183 [inline]
 kasan_check_range+0xef/0x1a0 mm/kasan/generic.c:189
 instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
 atomic_dec include/linux/atomic/atomic-instrumented.h:592 [inline]
 recv_work+0x694/0xa80 drivers/block/nbd.c:1022
 process_one_work+0x9cc/0x1b70 kernel/workqueue.c:3238
 process_scheduled_works kernel/workqueue.c:3319 [inline]
 worker_thread+0x6c8/0xf10 kernel/workqueue.c:3400
 kthread+0x3c2/0x780 kernel/kthread.c:464
 ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:153
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 

nbd_genl_connect() does not properly stop the device on certain
error paths after nbd_start_device() has been called. This causes
the error path to put nbd->config while recv_work continue to use
the config after putting it, leading to use-after-free in recv_work.

This patch moves nbd_start_device() after the backend file creation.

Reported-by: syzbot+48240bab47e705c53126@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/68227a04.050a0220.f2294.00b5.GAE@google.com/T/
Fixes: 6497ef8df568 ("nbd: provide a way for userspace processes to identify device backends")
Signed-off-by: Zheng Qixing 
Reviewed-by: Yu Kuai 
Link: https://lore.kernel.org/r/20250612132405.364904-1-zhengqixing@huaweicloud.com
Signed-off-by: Jens Axboe 
Signed-off-by: Sasha Levin

nbd: don't allow reconnect after disconnect

2025-03-13T11:49:51+00:00

[ Upstream commit 844b8cdc681612ff24df62cdefddeab5772fadf1 ]

Following process can cause nbd_config UAF:

1) grab nbd_config temporarily;

2) nbd_genl_disconnect() flush all recv_work() and release the
initial reference:

  nbd_genl_disconnect
   nbd_disconnect_and_put
    nbd_disconnect
     flush_workqueue(nbd->recv_workq)
    if (test_and_clear_bit(NBD_RT_HAS_CONFIG_REF, ...))
     nbd_config_put
     -> due to step 1), reference is still not zero

3) nbd_genl_reconfigure() queue recv_work() again;

  nbd_genl_reconfigure
   config = nbd_get_config_unlocked(nbd)
   if (!config)
   -> succeed
   if (!test_bit(NBD_RT_BOUND, ...))
   -> succeed
   nbd_reconnect_socket
    queue_work(nbd->recv_workq, &args->work)

4) step 1) release the reference;

5) Finially, recv_work() will trigger UAF:

  recv_work
   nbd_config_put(nbd)
   -> nbd_config is freed
   atomic_dec(&config->recv_threads)
   -> UAF

Fix the problem by clearing NBD_RT_BOUND in nbd_genl_disconnect(), so
that nbd_genl_reconfigure() will fail.

Fixes: b7aa3d39385d ("nbd: add a reconfigure netlink command")
Reported-by: syzbot+6b0df248918b92c33e6a@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/675bfb65.050a0220.1a2d0d.0006.GAE@google.com/
Signed-off-by: Yu Kuai 
Reviewed-by: Christoph Hellwig 
Link: https://lore.kernel.org/r/20250103092859.3574648-1-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe 
Signed-off-by: Sasha Levin

nbd: null check for nla_nest_start

2024-03-26T22:21:14+00:00

[ Upstream commit 31edf4bbe0ba27fd03ac7d87eb2ee3d2a231af6d ]

nla_nest_start() may fail and return NULL. Insert a check and set errno
based on other call sites within the same source code.

Signed-off-by: Navid Emamdoost 
Reviewed-by: Michal Kubecek 
Fixes: 47d902b90a32 ("nbd: add a status netlink command")
Signed-off-by: Kees Cook 
Link: https://lore.kernel.org/r/20240218042534.it.206-kees@kernel.org
Signed-off-by: Jens Axboe 
Signed-off-by: Sasha Levin

nbd: Add the maximum limit of allocated index in nbd_dev_add

2024-03-01T12:21:54+00:00

[ Upstream commit f12bc113ce904777fd6ca003b473b427782b3dde ]

If the index allocated by idr_alloc greater than MINORMASK >> part_shift,
the device number will overflow, resulting in failure to create a block
device.

Fix it by imiting the size of the max allocation.

Signed-off-by: Zhong Jinghua 
Reviewed-by: Christoph Hellwig 
Link: https://lore.kernel.org/r/20230605122159.2134384-1-zhongjinghua@huaweicloud.com
Signed-off-by: Jens Axboe 
Signed-off-by: Sasha Levin

nbd: Fix debugfs_create_dir error checking

2023-06-09T08:32:21+00:00

[ Upstream commit 4913cfcf014c95f0437db2df1734472fd3e15098 ]

The debugfs_create_dir function returns ERR_PTR in case of error, and the
only correct way to check if an error occurred is 'IS_ERR' inline function.
This patch will replace the null-comparison with IS_ERR.

Signed-off-by: Ivan Orlov 
Link: https://lore.kernel.org/r/20230512130533.98709-1-ivan.orlov0322@gmail.com
Signed-off-by: Jens Axboe 
Signed-off-by: Sasha Levin

nbd: fix incomplete validation of ioctl arg

2023-05-24T16:36:46+00:00

[ Upstream commit 55793ea54d77719a071b1ccc05a05056e3b5e009 ]

We tested and found an alarm caused by nbd_ioctl arg without verification.
The UBSAN warning calltrace like below:

UBSAN: Undefined behaviour in fs/buffer.c:1709:35
signed integer overflow:
-9223372036854775808 - 1 cannot be represented in type 'long long int'
CPU: 3 PID: 2523 Comm: syz-executor.0 Not tainted 4.19.90 #1
Hardware name: linux,dummy-virt (DT)
Call trace:
 dump_backtrace+0x0/0x3f0 arch/arm64/kernel/time.c:78
 show_stack+0x28/0x38 arch/arm64/kernel/traps.c:158
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x170/0x1dc lib/dump_stack.c:118
 ubsan_epilogue+0x18/0xb4 lib/ubsan.c:161
 handle_overflow+0x188/0x1dc lib/ubsan.c:192
 __ubsan_handle_sub_overflow+0x34/0x44 lib/ubsan.c:206
 __block_write_full_page+0x94c/0xa20 fs/buffer.c:1709
 block_write_full_page+0x1f0/0x280 fs/buffer.c:2934
 blkdev_writepage+0x34/0x40 fs/block_dev.c:607
 __writepage+0x68/0xe8 mm/page-writeback.c:2305
 write_cache_pages+0x44c/0xc70 mm/page-writeback.c:2240
 generic_writepages+0xdc/0x148 mm/page-writeback.c:2329
 blkdev_writepages+0x2c/0x38 fs/block_dev.c:2114
 do_writepages+0xd4/0x250 mm/page-writeback.c:2344

The reason for triggering this warning is __block_write_full_page()
-> i_size_read(inode) - 1 overflow.
inode->i_size is assigned in __nbd_ioctl() -> nbd_set_size() -> bytesize.
We think it is necessary to limit the size of arg to prevent errors.

Moreover, __nbd_ioctl() -> nbd_add_socket(), arg will be cast to int.
Assuming the value of arg is 0x80000000000000001) (on a 64-bit machine),
it will become 1 after the coercion, which will return unexpected results.

Fix it by adding checks to prevent passing in too large numbers.

Signed-off-by: Zhong Jinghua 
Reviewed-by: Yu Kuai 
Reviewed-by: Josef Bacik 
Link: https://lore.kernel.org/r/20230206145805.2645671-1-zhongjinghua@huawei.com
Signed-off-by: Jens Axboe 
Signed-off-by: Sasha Levin