From: Greg KH <gregkh@linuxfoundation.org>
To: Kuniyuki Iwashima <kuniyu@google.com>
Cc: davem@davemloft.net, dsahern@kernel.org, edumazet@google.com,
horms@kernel.org, kuba@kernel.org, linux-kernel@vger.kernel.org,
netdev@vger.kernel.org, pabeni@redhat.com, stable@kernel.org
Subject: Re: [PATCH net] ipv6: rpl: expand skb head when recompressed SRH grows, not only on last segment
Date: Tue, 21 Apr 2026 07:50:45 +0200 [thread overview]
Message-ID: <2026042140-drench-pursuable-37fa@gregkh> (raw)
In-Reply-To: <20260421045510.1546375-1-kuniyu@google.com>
On Tue, Apr 21, 2026 at 04:52:52AM +0000, Kuniyuki Iwashima wrote:
> From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Date: Mon, 20 Apr 2026 21:32:25 +0200
> > ipv6_rpl_srh_rcv() processes a Routing Protocol for LLNs Source Routing
> > Header by decompressing it, swapping the next segment address into
> > ipv6_hdr->daddr, recompressing, and pushing the new header back. The
> > recompressed header can be larger than the original when the
> > address-elision opportunities are worse after the swap.
> >
> > The function pulls (hdr->hdrlen + 1) << 3 bytes (the old header) and
> > pushes (chdr->hdrlen + 1) << 3 + sizeof(ipv6hdr) bytes (the new header
> > plus the IPv6 header). pskb_expand_head() is called to guarantee
> > headroom only when segments_left == 0.
> >
> > A crafted SRH that loops back to the local host (each segment is a local
> > address, so ip6_route_input() delivers it back to ipv6_rpl_srh_rcv())
> > with chdr growing on each pass exhausts headroom over several
> > iterations.
>
> How could this occur.. ? Did AI generate a repro or just
> flagged the possibility ?
It generated a reproducer which caused a crash which made me have to
create this patch. I'll dig it out of the huge pile of mess that was
sent to me and get it into a form that I can reply here to.
thanks,
greg k-h
next prev parent reply other threads:[~2026-04-21 5:50 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-20 19:32 [PATCH net] ipv6: rpl: expand skb head when recompressed SRH grows, not only on last segment Greg Kroah-Hartman
2026-04-21 4:52 ` Kuniyuki Iwashima
2026-04-21 5:50 ` Greg KH [this message]
2026-04-21 7:48 ` Greg KH
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