The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 7a3429bace0e08d94c39245631ea6bc109dafa49 Mon Sep 17 00:00:00 2001 From: David Ahern dsahern@kernel.org Date: Thu, 30 Dec 2021 17:36:31 -0700 Subject: [PATCH] ipv4: Check attribute length for RTA_GATEWAY in multipath route

syzbot reported uninit-value: ============================================================ BUG: KMSAN: uninit-value in fib_get_nhs+0xac4/0x1f80 net/ipv4/fib_semantics.c:708 fib_get_nhs+0xac4/0x1f80 net/ipv4/fib_semantics.c:708 fib_create_info+0x2411/0x4870 net/ipv4/fib_semantics.c:1453 fib_table_insert+0x45c/0x3a10 net/ipv4/fib_trie.c:1224 inet_rtm_newroute+0x289/0x420 net/ipv4/fib_frontend.c:886

Add helper to validate RTA_GATEWAY length before using the attribute.

Fixes: 4e902c57417c ("[IPv4]: FIB configuration using struct fib_config") Reported-by: syzbot+d4b9a2851cc3ce998741@syzkaller.appspotmail.com Signed-off-by: David Ahern dsahern@kernel.org Cc: Thomas Graf tgraf@suug.ch Signed-off-by: David S. Miller davem@davemloft.net

diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c index fde7797b5806..f1caa2c1c041 100644 --- a/net/ipv4/fib_semantics.c +++ b/net/ipv4/fib_semantics.c @@ -662,6 +662,19 @@ static int fib_count_nexthops(struct rtnexthop *rtnh, int remaining, return nhs; }

+static int fib_gw_from_attr(__be32 *gw, struct nlattr *nla, + struct netlink_ext_ack *extack) +{ + if (nla_len(nla) < sizeof(*gw)) { + NL_SET_ERR_MSG(extack, "Invalid IPv4 address in RTA_GATEWAY"); + return -EINVAL; + } + + *gw = nla_get_in_addr(nla); + + return 0; +} + /* only called when fib_nh is integrated into fib_info */ static int fib_get_nhs(struct fib_info *fi, struct rtnexthop *rtnh, int remaining, struct fib_config *cfg, @@ -704,7 +717,11 @@ static int fib_get_nhs(struct fib_info *fi, struct rtnexthop *rtnh, return -EINVAL; } if (nla) { - fib_cfg.fc_gw4 = nla_get_in_addr(nla); + ret = fib_gw_from_attr(&fib_cfg.fc_gw4, nla, + extack); + if (ret) + goto errout; + if (fib_cfg.fc_gw4) fib_cfg.fc_gw_family = AF_INET; } else if (nlav) { @@ -902,6 +919,7 @@ int fib_nh_match(struct net *net, struct fib_config *cfg, struct fib_info *fi, attrlen = rtnh_attrlen(rtnh); if (attrlen > 0) { struct nlattr *nla, *nlav, *attrs = rtnh_attrs(rtnh); + int err;

nla = nla_find(attrs, attrlen, RTA_GATEWAY); nlav = nla_find(attrs, attrlen, RTA_VIA); @@ -912,12 +930,17 @@ int fib_nh_match(struct net *net, struct fib_config *cfg, struct fib_info *fi, }

if (nla) { + __be32 gw; + + err = fib_gw_from_attr(&gw, nla, extack); + if (err) + return err; + if (nh->fib_nh_gw_family != AF_INET || - nla_get_in_addr(nla) != nh->fib_nh_gw4) + gw != nh->fib_nh_gw4) return 1; } else if (nlav) { struct fib_config cfg2; - int err;

err = fib_gw_from_via(&cfg2, nlav, extack); if (err)