kernel/linux.git/drivers/block/nbd.c, branch v6.19.11

Merge tag 'for-6.19/block-20251201' of git://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux

2025-12-04T03:26:18+00:00

Pull block updates from Jens Axboe: - Fix head insertion for mq-deadline, a regression from when priority support was added - Series simplifying and improving the ublk user copy code - Various ublk related cleanups - Fixup REQ_NOWAIT handling in loop/zloop, clearing NOWAIT when the request is punted to a thread for handling - Merge and then later revert loop dio nowait support, as it ended up causing excessive stack usage for when the inline issue code needs to dip back into the full file system code - Improve auto integrity code, making it less deadlock prone - Speedup polled IO handling, but manually managing the hctx lookups - Fixes for blk-throttle for SSD devices - Small series with fixes for the S390 dasd driver - Add support for caching zones, avoiding unnecessary report zone queries - MD pull requests via Yu: - fix null-ptr-dereference regression for dm-raid0 - fix IO hang for raid5 when array is broken with IO inflight - remove legacy 1s delay to speed up system shutdown - change maintainer's email address - data can be lost if array is created with different lbs devices, fix this problem and record lbs of the array in metadata - fix rcu protection for md_thread - fix mddev kobject lifetime regression - enable atomic writes for md-linear - some cleanups - bcache updates via Coly - remove useless discard and cache device code - improve usage of per-cpu workqueues - Reorganize the IO scheduler switching code, fixing some lockdep reports as well - Improve the block layer P2P DMA support - Add support to the block tracing code for zoned devices - Segment calculation improves, and memory alignment flexibility improvements - Set of prep and cleanups patches for ublk batching support. The actual batching hasn't been added yet, but helps shrink down the workload of getting that patchset ready for 6.20 - Fix for how the ps3 block driver handles segments offsets - Improve how block plugging handles batch tag allocations - nbd fixes for use-after-free of the configuration on device clear/put - Set of improvements and fixes for zloop - Add Damien as maintainer of the block zoned device code handling - Various other fixes and cleanups * tag 'for-6.19/block-20251201' of git://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux: (162 commits) block/rnbd: correct all kernel-doc complaints blk-mq: use queue_hctx in blk_mq_map_queue_type md: remove legacy 1s delay in md_notify_reboot md/raid5: fix IO hang when array is broken with IO inflight md: warn about updating super block failure md/raid0: fix NULL pointer dereference in create_strip_zones() for dm-raid sbitmap: fix all kernel-doc warnings ublk: add helper of __ublk_fetch() ublk: pass const pointer to ublk_queue_is_zoned() ublk: refactor auto buffer register in ublk_dispatch_req() ublk: add `union ublk_io_buf` with improved naming ublk: add parameter `struct io_uring_cmd *` to ublk_prep_auto_buf_reg() kfifo: add kfifo_alloc_node() helper for NUMA awareness blk-mq: fix potential uaf for 'queue_hw_ctx' blk-mq: use array manage hctx map instead of xarray ublk: prevent invalid access with DEBUG s390/dasd: Use scnprintf() instead of sprintf() s390/dasd: Move device name formatting into separate function s390/dasd: Remove unnecessary debugfs_create() return checks s390/dasd: Fix gendisk parent after copy pair swap ...

nbd: defer config unlock in nbd_genl_connect

2025-11-11T14:50:15+00:00

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

nbd: defer config put in recv_work

2025-11-08T13:37:54+00:00

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

nbd: don't copy kernel creds

2025-11-04T11:36:16+00:00

No need to copy kernel credentials. Link: https://patch.msgid.link/20251103-work-creds-init_cred-v1-6-cb3ec8711a6a@kernel.org Reviewed-by: Jens Axboe Signed-off-by: Christian Brauner

nbd: override creds to kernel when calling sock_{send,recv}msg()

2025-10-20T15:27:58+00:00

sock_{send,recv}msg() internally calls security_socket_{send,recv}msg(), which does security checks (e.g. SELinux) for socket access against the current task. However, _sock_xmit() in drivers/block/nbd.c may be called indirectly from a userspace syscall, where the NBD socket access would be incorrectly checked against the calling userspace task (which simply tries to read/write a file that happens to reside on an NBD device). To fix this, temporarily override creds to kernel ones before calling the sock_*() functions. This allows the security modules to recognize this as internal access by the kernel, which will normally be allowed. A way to trigger the issue is to do the following (on a system with SELinux set to enforcing): ### Create nbd device: truncate -s 256M /tmp/testfile nbd-server localhost:10809 /tmp/testfile ### Connect to the nbd server: nbd-client localhost ### Create mdraid array mdadm --create -l 1 -n 2 /dev/md/testarray /dev/nbd0 missing After these steps, assuming the SELinux policy doesn't allow the unexpected access pattern, errors will be visible on the kernel console: [ 142.204243] nbd0: detected capacity change from 0 to 524288 [ 165.189967] md: async del_gendisk mode will be removed in future, please upgrade to mdadm-4.5+ [ 165.252299] md/raid1:md127: active with 1 out of 2 mirrors [ 165.252725] md127: detected capacity change from 0 to 522240 [ 165.255434] block nbd0: Send control failed (result -13) [ 165.255718] block nbd0: Request send failed, requeueing [ 165.256006] block nbd0: Dead connection, failed to find a fallback [ 165.256041] block nbd0: Receive control failed (result -32) [ 165.256423] block nbd0: shutting down sockets [ 165.257196] I/O error, dev nbd0, sector 2048 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 2 [ 165.257736] Buffer I/O error on dev md127, logical block 0, async page read [ 165.258263] I/O error, dev nbd0, sector 2048 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 2 [ 165.259376] Buffer I/O error on dev md127, logical block 0, async page read [ 165.259920] I/O error, dev nbd0, sector 2048 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 2 [ 165.260628] Buffer I/O error on dev md127, logical block 0, async page read [ 165.261661] ldm_validate_partition_table(): Disk read failed. [ 165.262108] I/O error, dev nbd0, sector 2048 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 2 [ 165.262769] Buffer I/O error on dev md127, logical block 0, async page read [ 165.263697] I/O error, dev nbd0, sector 2048 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 2 [ 165.264412] Buffer I/O error on dev md127, logical block 0, async page read [ 165.265412] I/O error, dev nbd0, sector 2048 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 2 [ 165.265872] Buffer I/O error on dev md127, logical block 0, async page read [ 165.266378] I/O error, dev nbd0, sector 2048 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 2 [ 165.267168] Buffer I/O error on dev md127, logical block 0, async page read [ 165.267564] md127: unable to read partition table [ 165.269581] I/O error, dev nbd0, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 2 [ 165.269960] Buffer I/O error on dev nbd0, logical block 0, async page read [ 165.270316] I/O error, dev nbd0, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 2 [ 165.270913] Buffer I/O error on dev nbd0, logical block 0, async page read [ 165.271253] I/O error, dev nbd0, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 2 [ 165.271809] Buffer I/O error on dev nbd0, logical block 0, async page read [ 165.272074] ldm_validate_partition_table(): Disk read failed. [ 165.272360] nbd0: unable to read partition table [ 165.289004] ldm_validate_partition_table(): Disk read failed. [ 165.289614] nbd0: unable to read partition table The corresponding SELinux denial on Fedora/RHEL will look like this (assuming it's not silenced): type=AVC msg=audit(1758104872.510:116): avc: denied { write } for pid=1908 comm="mdadm" laddr=::1 lport=32772 faddr=::1 fport=10809 scontext=system_u:system_r:mdadm_t:s0-s0:c0.c1023 tcontext=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 tclass=tcp_socket permissive=0 The respective backtrace looks like this: @security[mdadm, -13, handshake_exit+221615650 handshake_exit+221615650 handshake_exit+221616465 security_socket_sendmsg+5 sock_sendmsg+106 handshake_exit+221616150 sock_sendmsg+5 __sock_xmit+162 nbd_send_cmd+597 nbd_handle_cmd+377 nbd_queue_rq+63 blk_mq_dispatch_rq_list+653 __blk_mq_do_dispatch_sched+184 __blk_mq_sched_dispatch_requests+333 blk_mq_sched_dispatch_requests+38 blk_mq_run_hw_queue+239 blk_mq_dispatch_plug_list+382 blk_mq_flush_plug_list.part.0+55 __blk_flush_plug+241 __submit_bio+353 submit_bio_noacct_nocheck+364 submit_bio_wait+84 __blkdev_direct_IO_simple+232 blkdev_read_iter+162 vfs_read+591 ksys_read+95 do_syscall_64+92 entry_SYSCALL_64_after_hwframe+120 ]: 1 The issue has started to appear since commit 060406c61c7c ("block: add plug while submitting IO"). Cc: Ming Lei Link: https://bugzilla.redhat.com/show_bug.cgi?id=2348878 Fixes: 060406c61c7c ("block: add plug while submitting IO") Signed-off-by: Ondrej Mosnacek Acked-by: Paul Moore Acked-by: Stephen Smalley Reviewed-by: Ming Lei Tested-by: Ming Lei Signed-off-by: Jens Axboe

drivers/block: replace use of system_wq with system_percpu_wq

2025-09-09T15:11:31+00:00

Currently if a user enqueue a work item using schedule_delayed_work() the used wq is "system_wq" (per-cpu wq) while queue_delayed_work() use WORK_CPU_UNBOUND (used when a cpu is not specified). The same applies to schedule_work() that is using system_wq and queue_work(), that makes use again of WORK_CPU_UNBOUND. This lack of consistentcy cannot be addressed without refactoring the API. system_unbound_wq should be the default workqueue so as not to enforce locality constraints for random work whenever it's not required. Adding system_dfl_wq to encourage its use when unbound work should be used. queue_work() / queue_delayed_work() / mod_delayed_work() will now use the new unbound wq: whether the user still use the old wq a warn will be printed along with a wq redirect to the new one. The old system_unbound_wq will be kept for a few release cycles. Suggested-by: Tejun Heo Signed-off-by: Marco Crivellari Signed-off-by: Jens Axboe

nbd: restrict sockets to TCP and UDP

2025-09-09T13:28:51+00:00

Recently, syzbot started to abuse NBD with all kinds of sockets. Commit cf1b2326b734 ("nbd: verify socket is supported during setup") made sure the socket supported a shutdown() method. Explicitely accept TCP and UNIX stream sockets. Fixes: cf1b2326b734 ("nbd: verify socket is supported during setup") Reported-by: syzbot+e1cd6bd8493060bd701d@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/CANn89iJ+76eE3A_8S_zTpSyW5hvPRn6V57458hCZGY5hbH_bFA@mail.gmail.com/T/#m081036e8747cd7e2626c1da5d78c8b9d1e55b154 Signed-off-by: Eric Dumazet Cc: Mike Christie Cc: Richard W.M. Jones Cc: Jens Axboe Cc: Yu Kuai Cc: linux-block@vger.kernel.org Cc: nbd@other.debian.org Signed-off-by: Jens Axboe

Merge tag 'for-6.17/block-20250728' of git://git.kernel.dk/linux

2025-07-28T23:43:54+00:00

Pull block updates from Jens Axboe: - MD pull request via Yu: - call del_gendisk synchronously (Xiao) - cleanup unused variable (John) - cleanup workqueue flags (Ryo) - fix faulty rdev can't be removed during resync (Qixing) - NVMe pull request via Christoph: - try PCIe function level reset on init failure (Keith Busch) - log TLS handshake failures at error level (Maurizio Lombardi) - pci-epf: do not complete commands twice if nvmet_req_init() fails (Rick Wertenbroek) - misc cleanups (Alok Tiwari) - Removal of the pktcdvd driver This has been more than a decade coming at this point, and some recently revealed breakages that had it causing issues even for cases where it isn't required made me re-pull the trigger on this one. It's known broken and nobody has stepped up to maintain the code - Series for ublk supporting batch commands, enabling the use of multishot where appropriate - Speed up ublk exit handling - Fix for the two-stage elevator fixing which could leak data - Convert NVMe to use the new IOVA based API - Increase default max transfer size to something more reasonable - Series fixing write operations on zoned DM devices - Add tracepoints for zoned block device operations - Prep series working towards improving blk-mq queue management in the presence of isolated CPUs - Don't allow updating of the block size of a loop device that is currently under exclusively ownership/open - Set chunk sectors from stacked device stripe size and use it for the atomic write size limit - Switch to folios in bcache read_super() - Fix for CD-ROM MRW exit flush handling - Various tweaks, fixes, and cleanups * tag 'for-6.17/block-20250728' of git://git.kernel.dk/linux: (94 commits) block: restore two stage elevator switch while running nr_hw_queue update cdrom: Call cdrom_mrw_exit from cdrom_release function sunvdc: Balance device refcount in vdc_port_mpgroup_check nvme-pci: try function level reset on init failure dm: split write BIOs on zone boundaries when zone append is not emulated block: use chunk_sectors when evaluating stacked atomic write limits dm-stripe: limit chunk_sectors to the stripe size md/raid10: set chunk_sectors limit md/raid0: set chunk_sectors limit block: sanitize chunk_sectors for atomic write limits ilog2: add max_pow_of_two_factor() nvmet: pci-epf: Do not complete commands twice if nvmet_req_init() fails nvme-tcp: log TLS handshake failures at error level docs: nvme: fix grammar in nvme-pci-endpoint-target.rst nvme: fix typo in status code constant for self-test in progress nvmet: remove redundant assignment of error code in nvmet_ns_enable() nvme: fix incorrect variable in io cqes error message nvme: fix multiple spelling and grammar issues in host drivers block: fix blk_zone_append_update_request_bio() kernel-doc md/raid10: fix set but not used variable in sync_request_write() ...

nbd: fix lockdep deadlock warning

2025-07-09T22:50:05+00:00

nbd grabs device lock nbd->config_lock for updating nr_hw_queues, this ways cause the following lock dependency: -> #2 (&disk->open_mutex){+.+.}-{4:4}: lock_acquire kernel/locking/lockdep.c:5871 [inline] lock_acquire+0x1ac/0x448 kernel/locking/lockdep.c:5828 __mutex_lock_common kernel/locking/mutex.c:602 [inline] __mutex_lock+0x166/0x1292 kernel/locking/mutex.c:747 mutex_lock_nested+0x14/0x1c kernel/locking/mutex.c:799 __del_gendisk+0x132/0xac6 block/genhd.c:706 del_gendisk+0xf6/0x19a block/genhd.c:819 nbd_dev_remove+0x3c/0xf2 drivers/block/nbd.c:268 nbd_dev_remove_work+0x1c/0x26 drivers/block/nbd.c:284 process_one_work+0x96a/0x1f32 kernel/workqueue.c:3238 process_scheduled_works kernel/workqueue.c:3321 [inline] worker_thread+0x5ce/0xde8 kernel/workqueue.c:3402 kthread+0x39c/0x7d4 kernel/kthread.c:464 ret_from_fork_kernel+0x2a/0xbb2 arch/riscv/kernel/process.c:214 ret_from_fork_kernel_asm+0x16/0x18 arch/riscv/kernel/entry.S:327 -> #1 (&set->update_nr_hwq_lock){++++}-{4:4}: lock_acquire kernel/locking/lockdep.c:5871 [inline] lock_acquire+0x1ac/0x448 kernel/locking/lockdep.c:5828 down_write+0x9c/0x19a kernel/locking/rwsem.c:1577 blk_mq_update_nr_hw_queues+0x3e/0xb86 block/blk-mq.c:5041 nbd_start_device+0x140/0xb2c drivers/block/nbd.c:1476 nbd_genl_connect+0xae0/0x1b24 drivers/block/nbd.c:2201 genl_family_rcv_msg_doit+0x206/0x2e6 net/netlink/genetlink.c:1115 genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline] genl_rcv_msg+0x514/0x78e net/netlink/genetlink.c:1210 netlink_rcv_skb+0x206/0x3be net/netlink/af_netlink.c:2534 genl_rcv+0x36/0x4c net/netlink/genetlink.c:1219 netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline] netlink_unicast+0x4f0/0x82c net/netlink/af_netlink.c:1339 netlink_sendmsg+0x85e/0xdd6 net/netlink/af_netlink.c:1883 sock_sendmsg_nosec net/socket.c:712 [inline] __sock_sendmsg+0xcc/0x160 net/socket.c:727 ____sys_sendmsg+0x63e/0x79c net/socket.c:2566 ___sys_sendmsg+0x144/0x1e6 net/socket.c:2620 __sys_sendmsg+0x188/0x246 net/socket.c:2652 __do_sys_sendmsg net/socket.c:2657 [inline] __se_sys_sendmsg net/socket.c:2655 [inline] __riscv_sys_sendmsg+0x70/0xa2 net/socket.c:2655 syscall_handler+0x94/0x118 arch/riscv/include/asm/syscall.h:112 do_trap_ecall_u+0x396/0x530 arch/riscv/kernel/traps.c:341 handle_exception+0x146/0x152 arch/riscv/kernel/entry.S:197 -> #0 (&nbd->config_lock){+.+.}-{4:4}: check_noncircular+0x132/0x146 kernel/locking/lockdep.c:2178 check_prev_add kernel/locking/lockdep.c:3168 [inline] check_prevs_add kernel/locking/lockdep.c:3287 [inline] validate_chain kernel/locking/lockdep.c:3911 [inline] __lock_acquire+0x12b2/0x24ea kernel/locking/lockdep.c:5240 lock_acquire kernel/locking/lockdep.c:5871 [inline] lock_acquire+0x1ac/0x448 kernel/locking/lockdep.c:5828 __mutex_lock_common kernel/locking/mutex.c:602 [inline] __mutex_lock+0x166/0x1292 kernel/locking/mutex.c:747 mutex_lock_nested+0x14/0x1c kernel/locking/mutex.c:799 refcount_dec_and_mutex_lock+0x60/0xd8 lib/refcount.c:118 nbd_config_put+0x3a/0x610 drivers/block/nbd.c:1423 nbd_release+0x94/0x15c drivers/block/nbd.c:1735 blkdev_put_whole+0xac/0xee block/bdev.c:721 bdev_release+0x3fe/0x600 block/bdev.c:1144 blkdev_release+0x1a/0x26 block/fops.c:684 __fput+0x382/0xa8c fs/file_table.c:465 ____fput+0x1c/0x26 fs/file_table.c:493 task_work_run+0x16a/0x25e kernel/task_work.c:227 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline] exit_to_user_mode_loop+0x118/0x134 kernel/entry/common.c:114 exit_to_user_mode_prepare include/linux/entry-common.h:330 [inline] syscall_exit_to_user_mode_work include/linux/entry-common.h:414 [inline] syscall_exit_to_user_mode include/linux/entry-common.h:449 [inline] do_trap_ecall_u+0x3f0/0x530 arch/riscv/kernel/traps.c:355 handle_exception+0x146/0x152 arch/riscv/kernel/entry.S:197 Also it isn't necessary to require nbd->config_lock, because blk_mq_update_nr_hw_queues() does grab tagset lock for sync everything. Fixes the issue by releasing ->config_lock & retry in case of concurrent updating nr_hw_queues. Fixes: 98e68f67020c ("block: prevent adding/deleting disk during updating nr_hw_queues") Reported-by: syzbot+2bcecf3c38cb3e8fdc8d@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/6855034f.a00a0220.137b3.0031.GAE@google.com Reviewed-by: Yu Kuai Cc: Nilay Shroff Signed-off-by: Ming Lei Reviewed-by: Nilay Shroff Link: https://lore.kernel.org/r/20250709111744.2353050-1-ming.lei@redhat.com Signed-off-by: Jens Axboe

nbd: fix uaf in nbd_genl_connect() error path

2025-07-07T17:58:08+00:00

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