From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 47F282C0F97; Wed, 25 Feb 2026 06:56:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772002593; cv=none; b=SwnNB2g3KHLMOgO/jirORkxxIe8KFGI/uXK85jkECbXDmlvGs1bPSDqT3nTq6V+JaCjJWVi/NPWlmlRDWzYbSkg0TY/741vAnx4CpzaZ9R6WonPuQxtTt52Fto27UfkU0zY8tJ7wPRN5hnHwyqaEsOqVQ0ve+dB1i9C+WACIgOM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772002593; c=relaxed/simple; bh=p42xfq0UVJprT5HtP10XaYlea1B0iLDvbMGYVnl9Xyk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=V0PWKXqyytimfooEgAYuel5T4dGfpLh+iWXrI/NrxUc3qx3hKCpA2D+m6L5335y1Oi7V0PFeLmgwQpxCxXAQJoB73hG8Mb+FxdG5+SyRDIDYmxSjLOvD6VJh5b9zz/kiNtu9hNF0buisNQTsd8ZZMn0EHlf+f2wQFARVb4dI+Kg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=oRrlR/sE; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="oRrlR/sE" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D7113C116D0; Wed, 25 Feb 2026 06:56:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1772002592; bh=p42xfq0UVJprT5HtP10XaYlea1B0iLDvbMGYVnl9Xyk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=oRrlR/sEuS0sxgq8MxrAyGsNg6Pp0VPPr3CZcheWR4BWGWmeiY72MGIfVHPCRUJTq m2cdpLrpTP4Neu8oh0CWaiswCdDH085of6vmTR/072gWzsBmiUD2hOx/mNr9j4Ak/2 zbdOZvNkm7LmCaItBNsUU6IZRhYoBJhh81aGPcSo= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, syzbot+e738404dcd14b620923c@syzkaller.appspotmail.com, Jiayuan Chen , Jiayuan Chen , Paolo Abeni , Sasha Levin Subject: [PATCH 6.18 328/641] xfrm: fix ip_rt_bug race in icmp_route_lookup reverse path Date: Tue, 24 Feb 2026 17:20:54 -0800 Message-ID: <20260225012356.639686670@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260225012348.915798704@linuxfoundation.org> References: <20260225012348.915798704@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jiayuan Chen [ Upstream commit 81b84de32bb27ae1ae2eb9acf0420e9d0d14bf00 ] icmp_route_lookup() performs multiple route lookups to find a suitable route for sending ICMP error messages, with special handling for XFRM (IPsec) policies. The lookup sequence is: 1. First, lookup output route for ICMP reply (dst = original src) 2. Pass through xfrm_lookup() for policy check 3. If blocked (-EPERM) or dst is not local, enter "reverse path" 4. In reverse path, call xfrm_decode_session_reverse() to get fl4_dec which reverses the original packet's flow (saddr<->daddr swapped) 5. If fl4_dec.saddr is local (we are the original destination), use __ip_route_output_key() for output route lookup 6. If fl4_dec.saddr is NOT local (we are a forwarding node), use ip_route_input() to simulate the reverse packet's input path 7. Finally, pass rt2 through xfrm_lookup() with XFRM_LOOKUP_ICMP flag The bug occurs in step 6: ip_route_input() is called with fl4_dec.daddr (original packet's source) as destination. If this address becomes local between the initial check and ip_route_input() call (e.g., due to concurrent "ip addr add"), ip_route_input() returns a LOCAL route with dst.output set to ip_rt_bug. This route is then used for ICMP output, causing dst_output() to call ip_rt_bug(), triggering a WARN_ON: ------------[ cut here ]------------ WARNING: net/ipv4/route.c:1275 at ip_rt_bug+0x21/0x30, CPU#1 Call Trace: ip_push_pending_frames+0x202/0x240 icmp_push_reply+0x30d/0x430 __icmp_send+0x1149/0x24f0 ip_options_compile+0xa2/0xd0 ip_rcv_finish_core+0x829/0x1950 ip_rcv+0x2d7/0x420 __netif_receive_skb_one_core+0x185/0x1f0 netif_receive_skb+0x90/0x450 tun_get_user+0x3413/0x3fb0 tun_chr_write_iter+0xe4/0x220 ... Fix this by checking rt2->rt_type after ip_route_input(). If it's RTN_LOCAL, the route cannot be used for output, so treat it as an error. The reproducer requires kernel modification to widen the race window, making it unsuitable as a selftest. It is available at: https://gist.github.com/mrpre/eae853b72ac6a750f5d45d64ddac1e81 Reported-by: syzbot+e738404dcd14b620923c@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/000000000000b1060905eada8881@google.com/T/ Closes: https://lore.kernel.org/r/20260128090523.356953-1-jiayuan.chen@linux.dev Fixes: 8b7817f3a959 ("[IPSEC]: Add ICMP host relookup support") Signed-off-by: Jiayuan Chen Signed-off-by: Jiayuan Chen Link: https://patch.msgid.link/20260206050220.59642-1-jiayuan.chen@linux.dev Signed-off-by: Paolo Abeni Signed-off-by: Sasha Levin --- net/ipv4/icmp.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c index 8e10e9e7676c5..9323ee0a6ac48 100644 --- a/net/ipv4/icmp.c +++ b/net/ipv4/icmp.c @@ -554,6 +554,21 @@ static struct rtable *icmp_route_lookup(struct net *net, struct flowi4 *fl4, /* steal dst entry from skb_in, don't drop refcnt */ skb_dstref_steal(skb_in); skb_dstref_restore(skb_in, orefdst); + + /* + * At this point, fl4_dec.daddr should NOT be local (we + * checked fl4_dec.saddr above). However, a race condition + * may occur if the address is added to the interface + * concurrently. In that case, ip_route_input() returns a + * LOCAL route with dst.output=ip_rt_bug, which must not + * be used for output. + */ + if (!err && rt2 && rt2->rt_type == RTN_LOCAL) { + net_warn_ratelimited("detected local route for %pI4 during ICMP sending, src %pI4\n", + &fl4_dec.daddr, &fl4_dec.saddr); + dst_release(&rt2->dst); + err = -EINVAL; + } } if (err) -- 2.51.0