Re: [PATCH net] net: reject a forward path that loops back to the tunnel

ipip_fill_forward_path() and ip6_tnl_fill_forward_path() assign the outer
route's device to ctx->dev without checking that it differs from the tunnel
device itself.  When a tunnel's outer route resolves back to that same
tunnel, the walk in dev_fill_forward_path() makes no progress and trips its
loop check WARN_ON_ONCE(last_dev == ctx->dev). Release the route and
return -EOPNOTSUPP when the resolved dst device equals ctx->dev, so the
path walk either advances to a different device or fails cleanly.

Closes: https://lore.kernel.org/all/CA+0ovCgaRvbd0Udj70b2xxG8Cx3CaCpNhnf1V4RWQuDveZYZhA@mail.gmail.com/ (local)
Signed-off-by: Farhad Alemi <redacted>

Please add the missing Fixes tags. These appear to be the relevant
commits:

Fixes: ab427db178858 ("netfilter: flowtable: Add IPIP rx sw acceleration")
Fixes: d98103575dcdd ("netfilter: flowtable: Add IP6IP6 rx sw acceleration")

Thanks,
Xuanqiang