> In __vringh_iov(), the F_INDIRECT branch descends into the indirect
> table and continues before the descriptor accounting runs. A top-level
> indirect descriptor is therefore never charged to count. If such a
> descriptor sets NEXT to point back at itself, returning from the
> indirect table resumes at the same top-level descriptor, which is again
> not counted, so the walk never makes forward progress.
>
> Because count stays flat and indirect_count is reset to 0 on every
> return to the top-level table, neither bound in the loop check trips.
> A guest can spin the vringh worker at 100% CPU inside __vringh_iov(),
> an uninterruptible host DoS.
>
> Move the descriptor accounting above the indirect switch so that a
> top-level indirect descriptor is charged one top-level traversal step
> before the walk descends into its table, bringing this re-entry under
> the existing vrh->vring.num bound. Each top-level descriptor is still
> charged at most one step and indirect_count still bounds a single
> table, so legitimate chains (including the multiple-indirect case in
> tools/virtio/vringh_test.c) stay within vring.num, while a cyclic
> indirect descriptor is now rejected with -ELOOP.
>
> Fixes: dbd29e075228 ("vringh: Fix loop descriptors check in the indirect
> cases")
> Cc: Xie Yongji <[email protected]>
> Cc: [email protected]
> Assisted-by: Hawkeye:GLM-5.3-flash
> Assisted-by: Qoder:Qwen3.8-Max
> Signed-off-by: Fang Xieyan <[email protected]>
Sashiko has reviewed this patch and found no issues. It looks great!
--
Sashiko AI review ยท
https://sashiko.dev/#/patchset/[email protected]?part=1
