Re: [PATCH net v3 1/2] iov_iter: export iov_iter_restore

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] Exporting `iov_iter_restore` exposes a pre-existing logic error where restoring an `ITER_KVEC` iterator falsely triggers a `WARN_ON_ONCE`.
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commit b7b5854a768fd37654ad61552651a21df8d14c8f
Author: Octavian Purdila <tavip@google.com>

iov_iter: export iov_iter_restore

Export iov_iter_restore so that it can be used by modules. This is needed by
the virtio vsock transport to restore the msg_iter state when transmission
fails.

> diff --git a/lib/iov_iter.c b/lib/iov_iter.c
> index 273919b161617..f5df63961fb24 100644
> --- a/lib/iov_iter.c
> +++ b/lib/iov_iter.c
> @@ -1491,6 +1491,7 @@ void iov_iter_restore(struct iov_iter *i, struct iov_iter_state *state)
>  		i->__iov -= state->nr_segs - i->nr_segs;
>  	i->nr_segs = state->nr_segs;
>  }
> +EXPORT_SYMBOL_GPL(iov_iter_restore);

[Severity: High]
This isn't a bug introduced by this patch, but exporting this function to
modules exposes a pre-existing issue when restoring an ITER_KVEC iterator.

Looking at iov_iter_restore() in lib/iov_iter.c:

void iov_iter_restore(struct iov_iter *i, struct iov_iter_state *state)
{
	if (WARN_ON_ONCE(!iov_iter_is_bvec(i) && !iter_is_iovec(i) &&
			 !iter_is_ubuf(i)) && !iov_iter_is_kvec(i))
		return;

Because !iov_iter_is_kvec(i) is placed outside the WARN_ON_ONCE() parentheses,
restoring an ITER_KVEC evaluates to WARN_ON_ONCE(true) && false. This safely
skips the early return, but still incorrectly triggers the warning, which can
lead to a panic on systems with panic_on_warn enabled.

Since ITER_KVEC is often used for kernel-originated network and storage data,
does exporting this to modules like virtio vsock create a risk of falsely
triggering warnings or a denial of service condition?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260622222757.2130402-1-tavip@google.com?part=1