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 047C48F58; Mon, 4 Mar 2024 21:43:32 +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=1709588612; cv=none; b=MyDE0cWandepZMc4gEkSMKUxiNRdX1+L8ZhfO6UW2YPozknN/9khndGuU2BLfVc8JwLx1o4YSERVK4/RcrhKddWBI4AqzOXOdqeS62Kzm/+a/tV03zJ7cbeJIZzrkMQX/Si8qhzZke0I7qGMb+L2MaGT+I/iL0BV9XIqNmferv8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709588612; c=relaxed/simple; bh=1p7wvH2+dGnQ7S852jhSGCwbyw0/ocF3cB7SjeIJju0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=kG2hEA0eI2kB5aA5usyH0j3qP1uywzKhMlcXShQghSYFELuL6IRM5oD/8mAdx7yf16mjhl9S8FPUJ74Mfm6kArOs8VlPIeTIfl6+PBcscfSyg5+SZ3MBePn6lmV2YV/01yTWgmX3HEKXHusfmXIedN9qCfo1pEHpfEwSh/tdTR8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=vZhI6oAn; 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="vZhI6oAn" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8CD8FC433F1; Mon, 4 Mar 2024 21:43:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1709588611; bh=1p7wvH2+dGnQ7S852jhSGCwbyw0/ocF3cB7SjeIJju0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=vZhI6oAnjh1Spl2+7y/EiX4ySWOq2BOE9uET4n7B13v6vwrCRaitUDryQAv4Kgyhh nU8cLlMDgUXTQdhIVY0ujYvhsUzOZy1ijWJduUJrQod0IgSYAUEPBBq1muZeApBFDQ TLUdwgzTiX6bbdygXxhESNTwM2yS9z3yp3n1C8Zg= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Florian Westphal , Simon Horman , Jakub Kicinski , Sasha Levin , syzbot+bfde3bef047a81b8fde6@syzkaller.appspotmail.com Subject: [PATCH 6.1 030/215] net: ip_tunnel: prevent perpetual headroom growth Date: Mon, 4 Mar 2024 21:21:33 +0000 Message-ID: <20240304211557.944727006@linuxfoundation.org> X-Mailer: git-send-email 2.44.0 In-Reply-To: <20240304211556.993132804@linuxfoundation.org> References: <20240304211556.993132804@linuxfoundation.org> User-Agent: quilt/0.67 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 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Florian Westphal [ Upstream commit 5ae1e9922bbdbaeb9cfbe91085ab75927488ac0f ] syzkaller triggered following kasan splat: BUG: KASAN: use-after-free in __skb_flow_dissect+0x19d1/0x7a50 net/core/flow_dissector.c:1170 Read of size 1 at addr ffff88812fb4000e by task syz-executor183/5191 [..] kasan_report+0xda/0x110 mm/kasan/report.c:588 __skb_flow_dissect+0x19d1/0x7a50 net/core/flow_dissector.c:1170 skb_flow_dissect_flow_keys include/linux/skbuff.h:1514 [inline] ___skb_get_hash net/core/flow_dissector.c:1791 [inline] __skb_get_hash+0xc7/0x540 net/core/flow_dissector.c:1856 skb_get_hash include/linux/skbuff.h:1556 [inline] ip_tunnel_xmit+0x1855/0x33c0 net/ipv4/ip_tunnel.c:748 ipip_tunnel_xmit+0x3cc/0x4e0 net/ipv4/ipip.c:308 __netdev_start_xmit include/linux/netdevice.h:4940 [inline] netdev_start_xmit include/linux/netdevice.h:4954 [inline] xmit_one net/core/dev.c:3548 [inline] dev_hard_start_xmit+0x13d/0x6d0 net/core/dev.c:3564 __dev_queue_xmit+0x7c1/0x3d60 net/core/dev.c:4349 dev_queue_xmit include/linux/netdevice.h:3134 [inline] neigh_connected_output+0x42c/0x5d0 net/core/neighbour.c:1592 ... ip_finish_output2+0x833/0x2550 net/ipv4/ip_output.c:235 ip_finish_output+0x31/0x310 net/ipv4/ip_output.c:323 .. iptunnel_xmit+0x5b4/0x9b0 net/ipv4/ip_tunnel_core.c:82 ip_tunnel_xmit+0x1dbc/0x33c0 net/ipv4/ip_tunnel.c:831 ipgre_xmit+0x4a1/0x980 net/ipv4/ip_gre.c:665 __netdev_start_xmit include/linux/netdevice.h:4940 [inline] netdev_start_xmit include/linux/netdevice.h:4954 [inline] xmit_one net/core/dev.c:3548 [inline] dev_hard_start_xmit+0x13d/0x6d0 net/core/dev.c:3564 ... The splat occurs because skb->data points past skb->head allocated area. This is because neigh layer does: __skb_pull(skb, skb_network_offset(skb)); ... but skb_network_offset() returns a negative offset and __skb_pull() arg is unsigned. IOW, we skb->data gets "adjusted" by a huge value. The negative value is returned because skb->head and skb->data distance is more than 64k and skb->network_header (u16) has wrapped around. The bug is in the ip_tunnel infrastructure, which can cause dev->needed_headroom to increment ad infinitum. The syzkaller reproducer consists of packets getting routed via a gre tunnel, and route of gre encapsulated packets pointing at another (ipip) tunnel. The ipip encapsulation finds gre0 as next output device. This results in the following pattern: 1). First packet is to be sent out via gre0. Route lookup found an output device, ipip0. 2). ip_tunnel_xmit for gre0 bumps gre0->needed_headroom based on the future output device, rt.dev->needed_headroom (ipip0). 3). ip output / start_xmit moves skb on to ipip0. which runs the same code path again (xmit recursion). 4). Routing step for the post-gre0-encap packet finds gre0 as output device to use for ipip0 encapsulated packet. tunl0->needed_headroom is then incremented based on the (already bumped) gre0 device headroom. This repeats for every future packet: gre0->needed_headroom gets inflated because previous packets' ipip0 step incremented rt->dev (gre0) headroom, and ipip0 incremented because gre0 needed_headroom was increased. For each subsequent packet, gre/ipip0->needed_headroom grows until post-expand-head reallocations result in a skb->head/data distance of more than 64k. Once that happens, skb->network_header (u16) wraps around when pskb_expand_head tries to make sure that skb_network_offset() is unchanged after the headroom expansion/reallocation. After this skb_network_offset(skb) returns a different (and negative) result post headroom expansion. The next trip to neigh layer (or anything else that would __skb_pull the network header) makes skb->data point to a memory location outside skb->head area. v2: Cap the needed_headroom update to an arbitarily chosen upperlimit to prevent perpetual increase instead of dropping the headroom increment completely. Reported-and-tested-by: syzbot+bfde3bef047a81b8fde6@syzkaller.appspotmail.com Closes: https://groups.google.com/g/syzkaller-bugs/c/fL9G6GtWskY/m/VKk_PR5FBAAJ Fixes: 243aad830e8a ("ip_gre: include route header_len in max_headroom calculation") Signed-off-by: Florian Westphal Reviewed-by: Simon Horman Link: https://lore.kernel.org/r/20240220135606.4939-1-fw@strlen.de Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- net/ipv4/ip_tunnel.c | 28 +++++++++++++++++++++------- 1 file changed, 21 insertions(+), 7 deletions(-) diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c index 24961b304dad0..328f9068c6a43 100644 --- a/net/ipv4/ip_tunnel.c +++ b/net/ipv4/ip_tunnel.c @@ -540,6 +540,20 @@ static int tnl_update_pmtu(struct net_device *dev, struct sk_buff *skb, return 0; } +static void ip_tunnel_adj_headroom(struct net_device *dev, unsigned int headroom) +{ + /* we must cap headroom to some upperlimit, else pskb_expand_head + * will overflow header offsets in skb_headers_offset_update(). + */ + static const unsigned int max_allowed = 512; + + if (headroom > max_allowed) + headroom = max_allowed; + + if (headroom > READ_ONCE(dev->needed_headroom)) + WRITE_ONCE(dev->needed_headroom, headroom); +} + void ip_md_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, u8 proto, int tunnel_hlen) { @@ -614,13 +628,13 @@ void ip_md_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, } headroom += LL_RESERVED_SPACE(rt->dst.dev) + rt->dst.header_len; - if (headroom > READ_ONCE(dev->needed_headroom)) - WRITE_ONCE(dev->needed_headroom, headroom); - - if (skb_cow_head(skb, READ_ONCE(dev->needed_headroom))) { + if (skb_cow_head(skb, headroom)) { ip_rt_put(rt); goto tx_dropped; } + + ip_tunnel_adj_headroom(dev, headroom); + iptunnel_xmit(NULL, rt, skb, fl4.saddr, fl4.daddr, proto, tos, ttl, df, !net_eq(tunnel->net, dev_net(dev))); return; @@ -800,16 +814,16 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, max_headroom = LL_RESERVED_SPACE(rt->dst.dev) + sizeof(struct iphdr) + rt->dst.header_len + ip_encap_hlen(&tunnel->encap); - if (max_headroom > READ_ONCE(dev->needed_headroom)) - WRITE_ONCE(dev->needed_headroom, max_headroom); - if (skb_cow_head(skb, READ_ONCE(dev->needed_headroom))) { + if (skb_cow_head(skb, max_headroom)) { ip_rt_put(rt); dev->stats.tx_dropped++; kfree_skb(skb); return; } + ip_tunnel_adj_headroom(dev, max_headroom); + iptunnel_xmit(NULL, rt, skb, fl4.saddr, fl4.daddr, protocol, tos, ttl, df, !net_eq(tunnel->net, dev_net(dev))); return; -- 2.43.0