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Laurence Oberman
139f57343b
mpi3mr_refresh_tgtdevs() and mpi3mr_devinfochg_evt_bh() read tgt_dev->starget and immediately pass it to starget_for_each_device() without holding mrioc->tgtdev_lock. Every writer of this field -- mpi3mr_target_alloc(), mpi3mr_target_destroy(), mpi3mr_slave_destroy() and mpi3mr_sdev_init() -- correctly serializes access under tgtdev_lock, but these two read sites do not, which leaves a check-then-use window against the SCSI core's target teardown path (scsi_remove_target(), invoked e.g. via a concurrent host reset, sysfs "delete", or SCSI EH device offlining running independently of the fwevt workqueue). Sequence observed on production hardware, triggered on the mpi3mr0_fwevt_wrkr workqueue during a SAS topology change shortly after a controller reset: BUG: kernel NULL pointer dereference, address: 0000000000000058 RIP: scsi_is_host_device+0x7/0x20 Call Trace: starget_for_each_device+0x34/0x100 mpi3mr_refresh_tgtdevs+0x152/0x1d0 [mpi3mr] mpi3mr_fwevt_bh+0x514/0x6c0 [mpi3mr] mpi3mr_fwevt_worker+0x1a/0x50 [mpi3mr] process_one_work+0x194/0x380 worker_thread+0x2fe/0x410 mpi3mr_refresh_tgtdevs() reads tgt_dev->starget as non-NULL, but by the time starget_for_each_device() dereferences it, a concurrent mpi3mr_target_destroy() has already cleared tgt_dev->starget under tgtdev_lock and the SCSI/device core has freed the underlying scsi_target (and its embedded struct device). The stale pointer is then walked by dev_to_shost() -> scsi_is_host_device(), producing the NULL/garbage dereference above. Fix this by taking mrioc->tgtdev_lock around every read of tgt_dev->starget, matching the existing writer-side discipline. Since starget_for_each_device() and mpi3mr_update_sdev() can end up doing non-atomic work (e.g. queue_limits_commit_update()), the lock cannot be held across the whole call, so instead pin the target's device with get_device() while holding the lock, drop the lock, then run starget_for_each_device() against the pinned reference and put_device() afterwards. This closes the TOCTOU window instead of merely narrowing it. The same unlocked read-and-dereference pattern also exists earlier in mpi3mr_refresh_tgtdevs()'s first removal-scan loop (tgt_dev->starget->hostdata); fix it the same way by holding tgtdev_lock across that check, which is cheap since it only touches plain struct fields. Assisted-by: Claude:Sonnet5 [Claude Code] Signed-off-by: Laurence Oberman <loberman@redhat.com> Acked-by: Chandrakanth Patil <chandrakanth.patil@broadcom.com> Link: https://patch.msgid.link/20260831120047.14690-1-loberman@redhat.com Signed-off-by: Martin K. Petersen (Oracle) <mkp@kernel.org>