3.2.95-rc1 review patch. If anyone has any objections, please let me know.
------------------ From: Wei Wang <[email protected]> commit c5cff8561d2d0006e972bd114afd51f082fee77c upstream. 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 <[email protected]> Acked-by: Eric Dumazet <[email protected]> Acked-by: Martin KaFai Lau <[email protected]> Signed-off-by: David S. Miller <[email protected]> [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings <[email protected]> --- 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 @@ -63,6 +63,7 @@ struct fib6_node { __u16 fn_flags; __u32 fn_sernum; struct rt6_info *rr_ptr; + struct rcu_head rcu; }; #ifndef CONFIG_IPV6_SUBTREES @@ -126,9 +127,36 @@ static inline struct inet6_dev *ip6_dst_ return ((struct rt6_info *)dst)->rt6i_idev; } +/* 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) { - return rt->rt6i_node ? rt->rt6i_node->fn_sernum : 0; + u32 cookie = 0; + + rt6_get_cookie_safe(rt, &cookie); + + return cookie; } struct fib6_walker_t { --- a/net/ipv6/ip6_fib.c +++ b/net/ipv6/ip6_fib.c @@ -153,11 +153,23 @@ static __inline__ struct fib6_node * nod return fn; } -static __inline__ 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 __inline__ void rt6_release(struct rt6_info *rt) { if (atomic_dec_and_test(&rt->rt6i_ref)) @@ -529,9 +541,9 @@ insert_above: if (in == NULL || ln == NULL) { if (in) - node_free(in); + node_free_immediate(in); if (ln) - node_free(ln); + node_free_immediate(ln); return NULL; } @@ -743,7 +755,7 @@ int fib6_add(struct fib6_node *root, str root, and then (in st_failure) stale node in main tree. */ - node_free(sfn); + node_free_immediate(sfn); goto st_failure; } --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -964,10 +964,11 @@ struct dst_entry *ip6_blackhole_route(st static struct dst_entry *ip6_dst_check(struct dst_entry *dst, u32 cookie) { struct rt6_info *rt; + u32 rt_cookie; rt = (struct rt6_info *) dst; - if (rt->rt6i_node && (rt->rt6i_node->fn_sernum == cookie)) { + if (rt6_get_cookie_safe(rt, &rt_cookie) && rt_cookie == cookie) { if (rt->rt6i_peer_genid != rt6_peer_genid()) { if (!rt->rt6i_peer) rt6_bind_peer(rt, 0); @@ -1007,8 +1008,15 @@ static void ip6_link_failure(struct sk_b if (rt->rt6i_flags&RTF_CACHE) { dst_set_expires(&rt->dst, 0); rt->rt6i_flags |= RTF_EXPIRES; - } 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(); + } } }
