UBUNTU-CVE-2025-68372
In the Linux kernel, the following vulnerability has been resolved: nbd: defer config put in recv_work 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 Depends-on: e2daec488c57 ("nbd: Fix hungtask when nbd_config_put")
02 / AFFECTED SOFTWARE
Affected packages
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03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
In the Linux kernel, the following vulnerability has been resolved: nbd: defer config put in recv_work 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 Depends-on: e2daec488c57 ("nbd: Fix hungtask when nbd_config_put")
05 / REFERENCES
Further evidence
- https://git.kernel.org/stable/c/443a1721806b6ff6303b5229e9811d68172d622f
- https://git.kernel.org/stable/c/6b69593f72e1bfba6ca47ca8d9b619341fded7d6
- https://git.kernel.org/stable/c/742012f6bf29553fdc460bf646a58df3a7b43d01
- https://git.kernel.org/stable/c/9517b82d8d422d426a988b213fdd45c6b417b86d
- https://ubuntu.com/security/CVE-2025-68372
- https://ubuntu.com/security/notices/USN-8094-1
- https://ubuntu.com/security/notices/USN-8094-2
- https://ubuntu.com/security/notices/USN-8094-3
- https://ubuntu.com/security/notices/USN-8094-4
- https://ubuntu.com/security/notices/USN-8094-5
- https://ubuntu.com/security/notices/USN-8096-1
- https://ubuntu.com/security/notices/USN-8096-2
- https://ubuntu.com/security/notices/USN-8096-3
- https://ubuntu.com/security/notices/USN-8096-4
- https://ubuntu.com/security/notices/USN-8096-5
- https://ubuntu.com/security/notices/USN-8116-1
- https://ubuntu.com/security/notices/USN-8141-1
- https://ubuntu.com/security/notices/USN-8152-1
- https://ubuntu.com/security/notices/USN-8163-1
- https://ubuntu.com/security/notices/USN-8163-2
- https://ubuntu.com/security/notices/USN-8179-1
- https://ubuntu.com/security/notices/USN-8179-2
- https://ubuntu.com/security/notices/USN-8179-3
- https://ubuntu.com/security/notices/USN-8179-4
- https://ubuntu.com/security/notices/USN-8184-1
- https://ubuntu.com/security/notices/USN-8185-1
- https://ubuntu.com/security/notices/USN-8185-2
- https://ubuntu.com/security/notices/USN-8203-1
- https://ubuntu.com/security/notices/USN-8204-1
- https://ubuntu.com/security/notices/USN-8243-1
- https://ubuntu.com/security/notices/USN-8258-1
- https://ubuntu.com/security/notices/USN-8260-1
- https://ubuntu.com/security/notices/USN-8261-1
- https://ubuntu.com/security/notices/USN-8265-1
- https://ubuntu.com/security/notices/USN-8440-1
- https://www.cve.org/CVERecord?id=CVE-2025-68372