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kvm/vfio: ensure kvg instance stays around in kvm_vfio_group_add()
[ Upstream commit 9e0f4f2 ] kvm_vfio_group_add() creates kvg instance, links it to kv->group_list, and calls kvm_vfio_file_set_kvm() with kvg->file as an argument after dropping kv->lock. If we race group addition and deletion calls, kvg instance may get freed by the time we get around to calling kvm_vfio_file_set_kvm(). Previous iterations of the code did not reference kvg->file outside of the critical section, but used a temporary variable. Still, they had similar problem of the file reference being owned by kvg structure and potential for kvm_vfio_group_del() dropping it before kvm_vfio_group_add() had a chance to complete. Fix this by moving call to kvm_vfio_file_set_kvm() under the protection of kv->lock. We already call it while holding the same lock when vfio group is being deleted, so it should be safe here as well. Fixes: 2fc1bec ("kvm: set/clear kvm to/from vfio_group when group add/delete") Reviewed-by: Alex Williamson <[email protected]> Signed-off-by: Dmitry Torokhov <[email protected]> Reviewed-by: Kevin Tian <[email protected]> Link: https://lore.kernel.org/r/[email protected] Signed-off-by: Alex Williamson <[email protected]> Signed-off-by: Sasha Levin <[email protected]>
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