This is a note to let you know that I've just added the patch titled ipv6: add rcu grace period before freeing fib6_node to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: ipv6-add-rcu-grace-period-before-freeing-fib6_node.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From foo@baz Thu Sep 14 23:20:08 PDT 2017 From: Wei Wang <weiwan@xxxxxxxxxx> Date: Mon, 21 Aug 2017 09:47:10 -0700 Subject: ipv6: add rcu grace period before freeing fib6_node From: Wei Wang <weiwan@xxxxxxxxxx> [ Upstream commit c5cff8561d2d0006e972bd114afd51f082fee77c ] We currently keep rt->rt6i_node pointing to the fib6_node for the route. And some functions make use of this pointer to dereference the fib6_node from rt structure, e.g. rt6_check(). However, as there is neither refcount nor rcu taken when dereferencing rt->rt6i_node, it could potentially cause crashes as rt->rt6i_node could be set to NULL by other CPUs when doing a route deletion. This patch introduces an rcu grace period before freeing fib6_node and makes sure the functions that dereference it takes rcu_read_lock(). Note: there is no "Fixes" tag because this bug was there in a very early stage. Signed-off-by: Wei Wang <weiwan@xxxxxxxxxx> Acked-by: Eric Dumazet <edumazet@xxxxxxxxxx> Acked-by: Martin KaFai Lau <kafai@xxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- include/net/ip6_fib.h | 30 +++++++++++++++++++++++++++++- net/ipv6/ip6_fib.c | 20 ++++++++++++++++---- net/ipv6/route.c | 14 +++++++++++--- 3 files changed, 56 insertions(+), 8 deletions(-) --- a/include/net/ip6_fib.h +++ b/include/net/ip6_fib.h @@ -68,6 +68,7 @@ struct fib6_node { __u16 fn_flags; int fn_sernum; struct rt6_info *rr_ptr; + struct rcu_head rcu; }; #ifndef CONFIG_IPV6_SUBTREES @@ -165,13 +166,40 @@ static inline void rt6_update_expires(st rt0->rt6i_flags |= RTF_EXPIRES; } +/* Function to safely get fn->sernum for passed in rt + * and store result in passed in cookie. + * Return true if we can get cookie safely + * Return false if not + */ +static inline bool rt6_get_cookie_safe(const struct rt6_info *rt, + u32 *cookie) +{ + struct fib6_node *fn; + bool status = false; + + rcu_read_lock(); + fn = rcu_dereference(rt->rt6i_node); + + if (fn) { + *cookie = fn->fn_sernum; + status = true; + } + + rcu_read_unlock(); + return status; +} + static inline u32 rt6_get_cookie(const struct rt6_info *rt) { + u32 cookie = 0; + if (rt->rt6i_flags & RTF_PCPU || (unlikely(rt->dst.flags & DST_NOCACHE) && rt->dst.from)) rt = (struct rt6_info *)(rt->dst.from); - return rt->rt6i_node ? rt->rt6i_node->fn_sernum : 0; + rt6_get_cookie_safe(rt, &cookie); + + return cookie; } static inline void ip6_rt_put(struct rt6_info *rt) --- a/net/ipv6/ip6_fib.c +++ b/net/ipv6/ip6_fib.c @@ -148,11 +148,23 @@ static struct fib6_node *node_alloc(void return fn; } -static void node_free(struct fib6_node *fn) +static void node_free_immediate(struct fib6_node *fn) +{ + kmem_cache_free(fib6_node_kmem, fn); +} + +static void node_free_rcu(struct rcu_head *head) { + struct fib6_node *fn = container_of(head, struct fib6_node, rcu); + kmem_cache_free(fib6_node_kmem, fn); } +static void node_free(struct fib6_node *fn) +{ + call_rcu(&fn->rcu, node_free_rcu); +} + static void rt6_rcu_free(struct rt6_info *rt) { call_rcu(&rt->dst.rcu_head, dst_rcu_free); @@ -589,9 +601,9 @@ insert_above: if (!in || !ln) { if (in) - node_free(in); + node_free_immediate(in); if (ln) - node_free(ln); + node_free_immediate(ln); return ERR_PTR(-ENOMEM); } @@ -1020,7 +1032,7 @@ int fib6_add(struct fib6_node *root, str root, and then (in failure) stale node in main tree. */ - node_free(sfn); + node_free_immediate(sfn); err = PTR_ERR(sn); goto failure; } --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -1267,7 +1267,9 @@ static void rt6_dst_from_metrics_check(s static struct dst_entry *rt6_check(struct rt6_info *rt, u32 cookie) { - if (!rt->rt6i_node || (rt->rt6i_node->fn_sernum != cookie)) + u32 rt_cookie; + + if (!rt6_get_cookie_safe(rt, &rt_cookie) || rt_cookie != cookie) return NULL; if (rt6_check_expired(rt)) @@ -1335,8 +1337,14 @@ static void ip6_link_failure(struct sk_b if (rt->rt6i_flags & RTF_CACHE) { dst_hold(&rt->dst); ip6_del_rt(rt); - } else if (rt->rt6i_node && (rt->rt6i_flags & RTF_DEFAULT)) { - rt->rt6i_node->fn_sernum = -1; + } else { + struct fib6_node *fn; + + rcu_read_lock(); + fn = rcu_dereference(rt->rt6i_node); + if (fn && (rt->rt6i_flags & RTF_DEFAULT)) + fn->fn_sernum = -1; + rcu_read_unlock(); } } } Patches currently in stable-queue which might be from weiwan@xxxxxxxxxx are queue-4.9/ipv6-fix-sparse-warning-on-rt6i_node.patch queue-4.9/tcp-initialize-rcv_mss-to-tcp_min_mss-instead-of-0.patch queue-4.9/ipv6-add-rcu-grace-period-before-freeing-fib6_node.patch