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Tsirkin" , Jason Wang , Xuan Zhuo , =?UTF-8?q?Eugenio=20P=C3=A9rez?= Cc: Ammar Faizi , Yichun Zhang , Jiri Pirko , Yuka , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , Jiri Pirko , David Hildenbrand , virtualization@lists.linux.dev, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, gwml@gnuweeb.org, stable@vger.kernel.org Subject: [PATCH] virtio_pci: fix vq info pointer lookup via wrong index Date: Sun, 15 Mar 2026 21:18:08 +0700 Message-Id: <20260315141808.547081-1-ammarfaizi2@openresty.com> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit List-Id: Unbinding a virtio balloon device: echo virtio0 > /sys/bus/virtio/drivers/virtio_balloon/unbind triggers a NULL pointer dereference. The dmesg says: BUG: kernel NULL pointer dereference, address: 0000000000000008 [...] RIP: 0010:__list_del_entry_valid_or_report+0x5/0xf0 Call Trace: vp_del_vqs+0x121/0x230 remove_common+0x135/0x150 virtballoon_remove+0xee/0x100 virtio_dev_remove+0x3b/0x80 device_release_driver_internal+0x187/0x2c0 unbind_store+0xb9/0xe0 kernfs_fop_write_iter.llvm.11660790530567441834+0xf6/0x180 vfs_write+0x2a9/0x3b0 ksys_write+0x5c/0xd0 do_syscall_64+0x54/0x230 entry_SYSCALL_64_after_hwframe+0x29/0x31 [...] The virtio_balloon device registers 5 queues (inflate, deflate, stats, free_page, reporting) but only the first two are unconditional. The stats, free_page and reporting queues are each conditional on their respective feature bits. When any of these features are absent, the corresponding vqs_info entry has name == NULL, creating holes in the array. The root cause is an indexing mismatch introduced when vq info storage was changed to be passed as an argument. vp_find_vqs_msix() and vp_find_vqs_intx() store the info pointer at vp_dev->vqs[i], where 'i' is the caller's sparse array index. However, the virtqueue itself gets vq->index assigned from queue_idx, a dense index that skips NULL entries. When holes exist, 'i' and queue_idx diverge. Later, vp_del_vqs() looks up info via vp_dev->vqs[vq->index] using the dense index into the sparsely-populated array, and hits NULL. Fix this by storing info at vp_dev->vqs[queue_idx] instead of vp_dev->vqs[i], so the store index matches the lookup index (vq->index). Apply the fix to both the MSIX and INTX paths. Cc: Yichun Zhang Cc: Jiri Pirko Cc: stable@vger.kernel.org # v6.11+ Tested-by: Yuka Fixes: 89a1c435aec2 ("virtio_pci: pass vq info as an argument to vp_setup_vq()") Signed-off-by: Ammar Faizi --- drivers/virtio/virtio_pci_common.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c index da97b6a988de..164f480b18a6 100644 --- a/drivers/virtio/virtio_pci_common.c +++ b/drivers/virtio/virtio_pci_common.c @@ -414,28 +414,29 @@ static int vp_find_vqs_msix(struct virtio_device *vdev, unsigned int nvqs, err = vp_request_msix_vectors(vdev, nvectors, per_vq_vectors, desc); if (err) goto error_find; vp_dev->per_vq_vectors = per_vq_vectors; allocated_vectors = vp_dev->msix_used_vectors; for (i = 0; i < nvqs; ++i) { vqi = &vqs_info[i]; if (!vqi->name) { vqs[i] = NULL; continue; } - vqs[i] = vp_find_one_vq_msix(vdev, queue_idx++, vqi->callback, + vqs[i] = vp_find_one_vq_msix(vdev, queue_idx, vqi->callback, vqi->name, vqi->ctx, false, &allocated_vectors, vector_policy, - &vp_dev->vqs[i]); + &vp_dev->vqs[queue_idx]); + queue_idx++; if (IS_ERR(vqs[i])) { err = PTR_ERR(vqs[i]); goto error_find; } } if (!avq_num) return 0; sprintf(avq->name, "avq.%u", avq->vq_index); vq = vp_find_one_vq_msix(vdev, avq->vq_index, vp_modern_avq_done, avq->name, false, true, &allocated_vectors, vector_policy, &vp_dev->admin_vq.info); @@ -476,27 +477,28 @@ static int vp_find_vqs_intx(struct virtio_device *vdev, unsigned int nvqs, if (err) goto out_del_vqs; vp_dev->intx_enabled = 1; vp_dev->per_vq_vectors = false; for (i = 0; i < nvqs; ++i) { struct virtqueue_info *vqi = &vqs_info[i]; if (!vqi->name) { vqs[i] = NULL; continue; } - vqs[i] = vp_setup_vq(vdev, queue_idx++, vqi->callback, + vqs[i] = vp_setup_vq(vdev, queue_idx, vqi->callback, vqi->name, vqi->ctx, - VIRTIO_MSI_NO_VECTOR, &vp_dev->vqs[i]); + VIRTIO_MSI_NO_VECTOR, &vp_dev->vqs[queue_idx]); + queue_idx++; if (IS_ERR(vqs[i])) { err = PTR_ERR(vqs[i]); goto out_del_vqs; } } if (!avq_num) return 0; sprintf(avq->name, "avq.%u", avq->vq_index); vq = vp_setup_vq(vdev, queue_idx++, vp_modern_avq_done, avq->name, false, VIRTIO_MSI_NO_VECTOR, &vp_dev->admin_vq.info); -- Ammar Faizi