From c62d125accce505937b33bd393e1b02193d45e6f Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Mon, 11 Dec 2017 07:17:39 -0800 Subject: [PATCH] ipv4: igmp: guard against silly MTU values MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit [ Upstream commit b5476022bbada3764609368f03329ca287528dc8 ] IPv4 stack reacts to changes to small MTU, by disabling itself under RTNL. But there is a window where threads not using RTNL can see a wrong device mtu. This can lead to surprises, in igmp code where it is assumed the mtu is suitable. Fix this by reading device mtu once and checking IPv4 minimal MTU. This patch adds missing IPV4_MIN_MTU define, to not abuse ETH_MIN_MTU anymore. Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- include/net/ip.h | 2 ++ net/ipv4/devinet.c | 2 +- net/ipv4/igmp.c | 24 +++++++++++++++--------- net/ipv4/ip_tunnel.c | 4 ++-- 4 files changed, 20 insertions(+), 12 deletions(-) diff --git a/include/net/ip.h b/include/net/ip.h index c02d09be8ad0..6922e1ea084a 100644 --- a/include/net/ip.h +++ b/include/net/ip.h @@ -31,6 +31,8 @@ #include #include +#define IPV4_MIN_MTU 68 /* RFC 791 */ + struct sock; struct inet_skb_parm { diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c index 7c56b5aa60d5..4fcd016a2fd5 100644 --- a/net/ipv4/devinet.c +++ b/net/ipv4/devinet.c @@ -1322,7 +1322,7 @@ skip: static bool inetdev_valid_mtu(unsigned int mtu) { - return mtu >= 68; + return mtu >= IPV4_MIN_MTU; } static void inetdev_send_gratuitous_arp(struct net_device *dev, diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c index eab5cb74b174..d3a65343c417 100644 --- a/net/ipv4/igmp.c +++ b/net/ipv4/igmp.c @@ -412,16 +412,17 @@ static int grec_size(struct ip_mc_list *pmc, int type, int gdel, int sdel) } static struct sk_buff *add_grhead(struct sk_buff *skb, struct ip_mc_list *pmc, - int type, struct igmpv3_grec **ppgr) + int type, struct igmpv3_grec **ppgr, unsigned int mtu) { struct net_device *dev = pmc->interface->dev; struct igmpv3_report *pih; struct igmpv3_grec *pgr; - if (!skb) - skb = igmpv3_newpack(dev, dev->mtu); - if (!skb) - return NULL; + if (!skb) { + skb = igmpv3_newpack(dev, mtu); + if (!skb) + return NULL; + } pgr = (struct igmpv3_grec *)skb_put(skb, sizeof(struct igmpv3_grec)); pgr->grec_type = type; pgr->grec_auxwords = 0; @@ -444,10 +445,15 @@ static struct sk_buff *add_grec(struct sk_buff *skb, struct ip_mc_list *pmc, struct igmpv3_grec *pgr = NULL; struct ip_sf_list *psf, *psf_next, *psf_prev, **psf_list; int scount, stotal, first, isquery, truncate; + unsigned int mtu; if (pmc->multiaddr == IGMP_ALL_HOSTS) return skb; + mtu = READ_ONCE(dev->mtu); + if (mtu < IPV4_MIN_MTU) + return skb; + isquery = type == IGMPV3_MODE_IS_INCLUDE || type == IGMPV3_MODE_IS_EXCLUDE; truncate = type == IGMPV3_MODE_IS_EXCLUDE || @@ -468,7 +474,7 @@ static struct sk_buff *add_grec(struct sk_buff *skb, struct ip_mc_list *pmc, AVAILABLE(skb) < grec_size(pmc, type, gdeleted, sdeleted)) { if (skb) igmpv3_sendpack(skb); - skb = igmpv3_newpack(dev, dev->mtu); + skb = igmpv3_newpack(dev, mtu); } } first = 1; @@ -495,12 +501,12 @@ static struct sk_buff *add_grec(struct sk_buff *skb, struct ip_mc_list *pmc, pgr->grec_nsrcs = htons(scount); if (skb) igmpv3_sendpack(skb); - skb = igmpv3_newpack(dev, dev->mtu); + skb = igmpv3_newpack(dev, mtu); first = 1; scount = 0; } if (first) { - skb = add_grhead(skb, pmc, type, &pgr); + skb = add_grhead(skb, pmc, type, &pgr, mtu); first = 0; } if (!skb) @@ -534,7 +540,7 @@ empty_source: igmpv3_sendpack(skb); skb = NULL; /* add_grhead will get a new one */ } - skb = add_grhead(skb, pmc, type, &pgr); + skb = add_grhead(skb, pmc, type, &pgr, mtu); } } if (pgr) diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c index 7150b4c8b608..b80b775357eb 100644 --- a/net/ipv4/ip_tunnel.c +++ b/net/ipv4/ip_tunnel.c @@ -380,8 +380,8 @@ static int ip_tunnel_bind_dev(struct net_device *dev) dev->needed_headroom = t_hlen + hlen; mtu -= (dev->hard_header_len + t_hlen); - if (mtu < 68) - mtu = 68; + if (mtu < IPV4_MIN_MTU) + mtu = IPV4_MIN_MTU; return mtu; }