From d3843fe5fd45be0e04a251a2cc68893c859a31bd Mon Sep 17 00:00:00 2001 From: Wei Wang Date: Fri, 6 Oct 2017 12:06:06 -0700 Subject: [PATCH] ipv6: replace dst_hold() with dst_hold_safe() in routing code With rwlock, it is safe to call dst_hold() in the read thread because read thread is guaranteed to be separated from write thread. However, after we replace rwlock with rcu, it is no longer safe to use dst_hold(). A dst might already have been deleted but is waiting for the rcu grace period to pass before freeing the memory when a read thread is trying to do dst_hold(). This could potentially cause double free issue. So this commit replaces all dst_hold() with dst_hold_safe() in all read thread to avoid this double free issue. And in order to make the code more compact, a new function ip6_hold_safe() is introduced. It calls dst_hold_safe() first, and if that fails, it will either fall back to hold and return net->ipv6.ip6_null_entry or set rt to NULL according to the caller's need. Signed-off-by: Wei Wang Signed-off-by: Martin KaFai Lau Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- net/ipv6/addrconf.c | 3 +- net/ipv6/route.c | 71 +++++++++++++++++++++++++++++++++------------ 2 files changed, 54 insertions(+), 20 deletions(-) diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c index 873afafddfc4..f86e931d555e 100644 --- a/net/ipv6/addrconf.c +++ b/net/ipv6/addrconf.c @@ -2333,7 +2333,8 @@ static struct rt6_info *addrconf_get_prefix_route(const struct in6_addr *pfx, continue; if ((rt->rt6i_flags & noflags) != 0) continue; - dst_hold(&rt->dst); + if (!dst_hold_safe(&rt->dst)) + rt = NULL; break; } out: diff --git a/net/ipv6/route.c b/net/ipv6/route.c index 941c062389d2..aeb349aea429 100644 --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -874,6 +874,23 @@ static struct fib6_node* fib6_backtrack(struct fib6_node *fn, } } +static bool ip6_hold_safe(struct net *net, struct rt6_info **prt, + bool null_fallback) +{ + struct rt6_info *rt = *prt; + + if (dst_hold_safe(&rt->dst)) + return true; + if (null_fallback) { + rt = net->ipv6.ip6_null_entry; + dst_hold(&rt->dst); + } else { + rt = NULL; + } + *prt = rt; + return false; +} + static struct rt6_info *ip6_pol_route_lookup(struct net *net, struct fib6_table *table, struct flowi6 *fl6, int flags) @@ -898,7 +915,9 @@ restart: if (rt_cache) rt = rt_cache; - dst_use(&rt->dst, jiffies); + if (ip6_hold_safe(net, &rt, true)) + dst_use_noref(&rt->dst, jiffies); + read_unlock_bh(&table->tb6_lock); trace_fib6_table_lookup(net, rt, table->tb6_id, fl6); @@ -1061,10 +1080,9 @@ static struct rt6_info *rt6_get_pcpu_route(struct rt6_info *rt) p = this_cpu_ptr(rt->rt6i_pcpu); pcpu_rt = *p; - if (pcpu_rt) { - dst_hold(&pcpu_rt->dst); + if (pcpu_rt && ip6_hold_safe(NULL, &pcpu_rt, false)) rt6_dst_from_metrics_check(pcpu_rt); - } + return pcpu_rt; } @@ -1625,12 +1643,17 @@ redo_rt6_select: if (rt_cache) rt = rt_cache; - if (rt == net->ipv6.ip6_null_entry || (rt->rt6i_flags & RTF_CACHE)) { - dst_use(&rt->dst, jiffies); + if (rt == net->ipv6.ip6_null_entry) { + read_unlock_bh(&table->tb6_lock); + dst_hold(&rt->dst); + trace_fib6_table_lookup(net, rt, table->tb6_id, fl6); + return rt; + } else if (rt->rt6i_flags & RTF_CACHE) { + if (ip6_hold_safe(net, &rt, true)) { + dst_use_noref(&rt->dst, jiffies); + rt6_dst_from_metrics_check(rt); + } read_unlock_bh(&table->tb6_lock); - - rt6_dst_from_metrics_check(rt); - trace_fib6_table_lookup(net, rt, table->tb6_id, fl6); return rt; } else if (unlikely((fl6->flowi6_flags & FLOWI_FLAG_KNOWN_NH) && @@ -1643,7 +1666,13 @@ redo_rt6_select: struct rt6_info *uncached_rt; - dst_use(&rt->dst, jiffies); + if (ip6_hold_safe(net, &rt, true)) { + dst_use_noref(&rt->dst, jiffies); + } else { + read_unlock_bh(&table->tb6_lock); + uncached_rt = rt; + goto uncached_rt_out; + } read_unlock_bh(&table->tb6_lock); uncached_rt = ip6_rt_cache_alloc(rt, &fl6->daddr, NULL); @@ -1659,6 +1688,7 @@ redo_rt6_select: dst_hold(&uncached_rt->dst); } +uncached_rt_out: trace_fib6_table_lookup(net, uncached_rt, table->tb6_id, fl6); return uncached_rt; @@ -1667,8 +1697,7 @@ redo_rt6_select: struct rt6_info *pcpu_rt; - rt->dst.lastuse = jiffies; - rt->dst.__use++; + dst_use_noref(&rt->dst, jiffies); pcpu_rt = rt6_get_pcpu_route(rt); if (pcpu_rt) { @@ -2130,7 +2159,7 @@ restart: } out: - dst_hold(&rt->dst); + ip6_hold_safe(net, &rt, true); read_unlock_bh(&table->tb6_lock); @@ -2841,7 +2870,8 @@ static int ip6_route_del(struct fib6_config *cfg, continue; if (cfg->fc_protocol && cfg->fc_protocol != rt->rt6i_protocol) continue; - dst_hold(&rt->dst); + if (!dst_hold_safe(&rt->dst)) + break; read_unlock_bh(&table->tb6_lock); /* if gateway was specified only delete the one hop */ @@ -3038,7 +3068,7 @@ static struct rt6_info *rt6_get_route_info(struct net *net, continue; if (!ipv6_addr_equal(&rt->rt6i_gateway, gwaddr)) continue; - dst_hold(&rt->dst); + ip6_hold_safe(NULL, &rt, false); break; } out: @@ -3096,7 +3126,7 @@ struct rt6_info *rt6_get_dflt_router(const struct in6_addr *addr, struct net_dev break; } if (rt) - dst_hold(&rt->dst); + ip6_hold_safe(NULL, &rt, false); read_unlock_bh(&table->tb6_lock); return rt; } @@ -3139,9 +3169,12 @@ restart: for (rt = table->tb6_root.leaf; rt; rt = rt->dst.rt6_next) { if (rt->rt6i_flags & (RTF_DEFAULT | RTF_ADDRCONF) && (!rt->rt6i_idev || rt->rt6i_idev->cnf.accept_ra != 2)) { - dst_hold(&rt->dst); - read_unlock_bh(&table->tb6_lock); - ip6_del_rt(rt); + if (dst_hold_safe(&rt->dst)) { + read_unlock_bh(&table->tb6_lock); + ip6_del_rt(rt); + } else { + read_unlock_bh(&table->tb6_lock); + } goto restart; } } -- 2.30.2