Add a case to tools/virtio/vringh_test.c that builds a top-level indirect descriptor whose NEXT points back at itself and checks that vringh_getdesc_user() rejects it with -ELOOP.
Without the preceding fix, the walk re-enters the same top-level descriptor without making forward progress: count stays flat, so the traversal limit is never reached and -ELOOP is never returned. With the fix, the top-level count advances on each re-entry and vringh_getdesc_user() returns -ELOOP once the traversal limit is reached. Use index 1 rather than 0 for the self-cycle, since returning from an indirect table is only performed for a positive up_next value. A self-cycle at index 0 would instead terminate the walk and would not reproduce the bug. Assisted-by: Hawkeye:GLM-5.3-flash Assisted-by: Qoder:Qwen3.8-Max Signed-off-by: Fang Xieyan <[email protected]> --- tools/virtio/vringh_test.c | 41 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 41 insertions(+) diff --git a/tools/virtio/vringh_test.c b/tools/virtio/vringh_test.c index 84961b9..2a5d7f7 100644 --- a/tools/virtio/vringh_test.c +++ b/tools/virtio/vringh_test.c @@ -458,6 +458,8 @@ int main(int argc, char *argv[]) int err; unsigned i; void *ret; + struct vring_desc *ind; + char *data; bool (*getrange)(struct vringh *vrh, u64 addr, struct vringh_range *r); bool fast_vringh = false, parallel = false; @@ -755,6 +757,45 @@ int main(int argc, char *argv[]) vringh_iov_cleanup(&riov); } + /* + * Regression test: a top-level indirect descriptor whose NEXT + * points back to itself must be rejected with -ELOOP instead of + * looping forever. Use index 1 rather than 0 so that returning + * from the indirect table re-enters the same top-level descriptor. + */ + ind = __user_addr_max - USER_MEM/2; + data = __user_addr_max - USER_MEM/4; + + /* Fresh ring and host state; resets last_avail_idx to 0. */ + vring_init(&vrh.vring, RINGSIZE, __user_addr_min, ALIGN); + vringh_init_user(&vrh, vdev.features, RINGSIZE, true, + vrh.vring.desc, vrh.vring.avail, vrh.vring.used); + + /* Single-entry indirect table pointing at valid data. */ + ind[0].addr = (unsigned long)data; + ind[0].len = 1; + ind[0].flags = 0; + + /* Top-level desc[1]: INDIRECT, and NEXT loops back to itself. */ + vrh.vring.desc[1].addr = (unsigned long)ind; + vrh.vring.desc[1].len = sizeof(*ind); + vrh.vring.desc[1].flags = VRING_DESC_F_INDIRECT | VRING_DESC_F_NEXT; + vrh.vring.desc[1].next = 1; + + /* Publish head 1 on the avail ring. */ + vrh.vring.avail->ring[0] = 1; + vrh.vring.avail->idx = 1; + + vringh_iov_init(&riov, host_riov, ARRAY_SIZE(host_riov)); + vringh_iov_init(&wiov, host_wiov, ARRAY_SIZE(host_wiov)); + + err = vringh_getdesc_user(&vrh, &riov, &wiov, getrange, &head); + if (err != -ELOOP) + errx(1, "self-referential indirect: %i not -ELOOP", err); + + vringh_iov_cleanup(&riov); + vringh_iov_cleanup(&wiov); + /* Don't leak memory... */ vring_del_virtqueue(vq); free(__user_addr_min); -- 2.50.1
