The RCU-protected codepaths (mpls_forward, mpls_dump_routes) can have an inconsistent view of platform_labels vs platform_label in case of a concurrent resize (resize_platform_label_table, under platform_mutex). This can lead to OOB accesses. This patch adds a seqcount, so that we get a consistent snapshot. Note that mpls_label_ok is also susceptible to this, so the check against RTA_DST in rtm_to_route_config, done outside platform_mutex, is not sufficient. This value gets passed to mpls_label_ok once more in both mpls_route_add and mpls_route_del, so there is no issue, but that additional check must not be removed. Reported-by: Yuan Tan Reported-by: Yifan Wu Reported-by: Juefei Pu Reported-by: Xin Liu Fixes: 7720c01f3f590 ("mpls: Add a sysctl to control the size of the mpls label table") Fixes: dde1b38e873c ("mpls: Convert mpls_dump_routes() to RCU.") Signed-off-by: Sabrina Dubroca --- include/net/netns/mpls.h | 1 + net/mpls/af_mpls.c | 29 +++++++++++++++++++++++++---- 2 files changed, 26 insertions(+), 4 deletions(-) diff --git a/include/net/netns/mpls.h b/include/net/netns/mpls.h index 6682e51513ef..2073cbac2afb 100644 --- a/include/net/netns/mpls.h +++ b/include/net/netns/mpls.h @@ -17,6 +17,7 @@ struct netns_mpls { size_t platform_labels; struct mpls_route __rcu * __rcu *platform_label; struct mutex platform_mutex; + seqcount_mutex_t platform_label_seq; struct ctl_table_header *ctl; }; diff --git a/net/mpls/af_mpls.c b/net/mpls/af_mpls.c index d5417688f69e..18d3da8ab384 100644 --- a/net/mpls/af_mpls.c +++ b/net/mpls/af_mpls.c @@ -83,14 +83,30 @@ static struct mpls_route *mpls_route_input(struct net *net, unsigned int index) return mpls_dereference(net, platform_label[index]); } +static struct mpls_route __rcu **mpls_platform_label_rcu(struct net *net, size_t *platform_labels) +{ + struct mpls_route __rcu **platform_label; + unsigned int sequence; + + do { + sequence = read_seqcount_begin(&net->mpls.platform_label_seq); + platform_label = rcu_dereference(net->mpls.platform_label); + *platform_labels = net->mpls.platform_labels; + } while (read_seqcount_retry(&net->mpls.platform_label_seq, sequence)); + + return platform_label; +} + static struct mpls_route *mpls_route_input_rcu(struct net *net, unsigned int index) { struct mpls_route __rcu **platform_label; + size_t platform_labels; + + platform_label = mpls_platform_label_rcu(net, &platform_labels); - if (index >= net->mpls.platform_labels) + if (index >= platform_labels) return NULL; - platform_label = rcu_dereference(net->mpls.platform_label); return rcu_dereference(platform_label[index]); } @@ -2240,8 +2256,7 @@ static int mpls_dump_routes(struct sk_buff *skb, struct netlink_callback *cb) if (index < MPLS_LABEL_FIRST_UNRESERVED) index = MPLS_LABEL_FIRST_UNRESERVED; - platform_label = rcu_dereference(net->mpls.platform_label); - platform_labels = net->mpls.platform_labels; + platform_label = mpls_platform_label_rcu(net, &platform_labels); if (filter.filter_set) flags |= NLM_F_DUMP_FILTERED; @@ -2645,8 +2660,12 @@ static int resize_platform_label_table(struct net *net, size_t limit) } /* Update the global pointers */ + local_bh_disable(); + write_seqcount_begin(&net->mpls.platform_label_seq); net->mpls.platform_labels = limit; rcu_assign_pointer(net->mpls.platform_label, labels); + write_seqcount_end(&net->mpls.platform_label_seq); + local_bh_enable(); mutex_unlock(&net->mpls.platform_mutex); @@ -2728,6 +2747,8 @@ static __net_init int mpls_net_init(struct net *net) int i; mutex_init(&net->mpls.platform_mutex); + seqcount_mutex_init(&net->mpls.platform_label_seq, &net->mpls.platform_mutex); + net->mpls.platform_labels = 0; net->mpls.platform_label = NULL; net->mpls.ip_ttl_propagate = 1; -- 2.51.2