From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=94.136.29.106 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793196709; b=B0yaMXTykCLgf0VEIUJnXAA7SCE6yZtBaxtwL4hkRiHYEuly8l8wNppZW5VKjoqdO+3p mWeZxVb7UqTNofO7yp3yG1NLI90u42Fj/o1Rl9CbQ8UY8ZQ0d6XykGEFIHJ/muIwapJen lrQGPt7V0R7BVBu47w5z6hIENz5lktmIzxOl0jhBEB+IyGYbNjF7O4Zq/U//JZ5ycqYtg 05xCwus1rH0hhPQGo0JH4Bg6FmgU3blRcC3WwV4efcwMbZaR4rIg1Wxbp1TvYm7rYjLR5 1g+ITaX9Uwp9Whr+zZoVbasQDaDuXXRxSkUEgEzA9qa/v7IEj92f7pAtgHxrrqdZb2g== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793196709; h=DMARC-Filter:Received:Date:From:To:Cc:Subject:Message-ID:References: MIME-Version:Content-Type:Content-Disposition:In-Reply-To:User-Agent: X-Bm-Milter-Handled:X-Bm-Transport-Timestamp; bh=Oas1iDvhjflqMxlRkG543vYH9mLSvNdodcghSDCtqRs=; b=XIbori+3vzNr9OobAqGnVnhomwk2ml/0FLbnc3EzNnK+l+UFJkheqoR5R7Z+6RobBGn7 UHR1mbjVe+Su1QyeobFcUbTnd3ETKbSJDqa6QBPK62eo3JiSvgk4cBNRKbvI8WcLi1HOW /d7GLVwfp06i84IySu4fUiQks8/cuV4HJNLdo6b+G1B0ZA+AeU3vOWPV5xhqGXmvxqgcF wV01SD7013ufbCEZSyMjwmpGZxz69fNgpsErAuLP2mfkL4odzVzOEl9BUXPTHNoVRTU+j U3iG9rSIH34HNcNy9hdHdntggYJCG07JsxfJiTXCpNFzjqDpNFxKbvKZjC4gc12o3Cw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none header.from=proxmox.com; spf=pass smtp.mailfrom=proxmox.com; arc=none smtp.remote-ip=94.136.29.106 Received: from proxmox-new.maurer-it.com (proxmox-new.maurer-it.com [94.136.29.106]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D8E91606A31A; Wed, 28 Oct 2026 14:11:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org D8E91606A31A Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=proxmox.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=proxmox.com Received: from proxmox-new.maurer-it.com (localhost.localdomain [127.0.0.1]) by proxmox-new.maurer-it.com (Proxmox) with ESMTP id 1AF694383A; Wed, 28 Oct 2026 15:11:46 +0100 (CET) Date: Wed, 28 Oct 2026 15:11:43 +0100 From: Gabriel Goller To: Tang Bin Cc: andrea.mayer@uniroma2.it, davem@davemloft.net, edumazet@kernel.org, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] seg6: fix OOB read in advance_nextseg when segments_left is 0 Message-ID: References: <20261028113141.2111-1-tangbin@cmss.chinamobile.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20261028113141.2111-1-tangbin@cmss.chinamobile.com> User-Agent: NeoMutt/20260504 X-Bm-Milter-Handled: 55990f41-d878-4baa-be0a-ee34c49e34d2 X-Bm-Transport-Timestamp: 1793196704580 On 28.10.2026 19:31, Tang Bin wrote: > advance_nextseg() decrements srh->segments_left and uses it to index > srh->segments without checking it is non-zero. seg6_validate_srh() permits > segments_left == 0, so a packet with SRH segments_left==0 reaching an End* > action underflows the u8 (255) and reads srh->segments[255] (~4KB out of > bounds); the read bytes are then used as the new IPv6 destination address > (info leak) or crash on unmapped memory. The decap path > (decap_and_validate) already checks segments_left > 0, but the standard > End/End.X/End.T/End.B6.Encap/End.BPF paths do not. Reject segments_left == > 0 before decrementing. > > Fixes: d7a669dd2f8b ("ipv6: sr: add helper functions for seg6local") > Cc: stable@vger.kernel.org > Signed-off-by: Tang Bin > --- > net/ipv6/seg6_local.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/net/ipv6/seg6_local.c b/net/ipv6/seg6_local.c > index 53f7b2452..1d8312467 100644 > --- a/net/ipv6/seg6_local.c > +++ b/net/ipv6/seg6_local.c > @@ -310,6 +310,10 @@ static struct ipv6_sr_hdr *advance_nextseg(struct sk_buff *skb, > /* skb_ensure_writable() may change skb pointers; evaluate srh again */ > srh = (struct ipv6_sr_hdr *)(skb->data + srhoff); > > + if (srh->segments_left == 0) { > + *reason = SKB_DROP_REASON_NOT_SPECIFIED; > + return NULL; > + } > srh->segments_left--; > addr = srh->segments + srh->segments_left; > ipv6_hdr(skb)->daddr = *addr; > -- > 2.52.0.windows.1 Can you show a codepath where it is possible to call advance_nextseg() with srh->segments_left being 0? End/End.X/End.T/End.B6.Encap/End.BPF behaviors call get_and_validate_srh(), which calls seg6_get_srh(skb, IP6_FH_F_SKIP_RH), which uses ipv6_find_hdr(), which skips all the segments_left=0 headers. Thanks, Gabriel