From 4512c43eac7e007d982e7ea45152ea6f3f4d1921 Mon Sep 17 00:00:00 2001 From: Wei Wang Date: Mon, 8 Jan 2018 10:34:00 -0800 Subject: [PATCH] ipv6: remove null_entry before adding default route In the current code, when creating a new fib6 table, tb6_root.leaf gets initialized to net->ipv6.ip6_null_entry. If a default route is being added with rt->rt6i_metric = 0xffffffff, fib6_add() will add this route after net->ipv6.ip6_null_entry. As null_entry is shared, it could cause problem. In order to fix it, set fn->leaf to NULL before calling fib6_add_rt2node() when trying to add the first default route. And reset fn->leaf to null_entry when adding fails or when deleting the last default route. syzkaller reported the following issue which is fixed by this commit: WARNING: suspicious RCU usage 4.15.0-rc5+ #171 Not tainted ----------------------------- net/ipv6/ip6_fib.c:1702 suspicious rcu_dereference_protected() usage! other info that might help us debug this: rcu_scheduler_active = 2, debug_locks = 1 4 locks held by swapper/0/0: #0: ((&net->ipv6.ip6_fib_timer)){+.-.}, at: [<00000000d43f631b>] lockdep_copy_map include/linux/lockdep.h:178 [inline] #0: ((&net->ipv6.ip6_fib_timer)){+.-.}, at: [<00000000d43f631b>] call_timer_fn+0x1c6/0x820 kernel/time/timer.c:1310 #1: (&(&net->ipv6.fib6_gc_lock)->rlock){+.-.}, at: [<000000002ff9d65c>] spin_lock_bh include/linux/spinlock.h:315 [inline] #1: (&(&net->ipv6.fib6_gc_lock)->rlock){+.-.}, at: [<000000002ff9d65c>] fib6_run_gc+0x9d/0x3c0 net/ipv6/ip6_fib.c:2007 #2: (rcu_read_lock){....}, at: [<0000000091db762d>] __fib6_clean_all+0x0/0x3a0 net/ipv6/ip6_fib.c:1560 #3: (&(&tb->tb6_lock)->rlock){+.-.}, at: [<000000009e503581>] spin_lock_bh include/linux/spinlock.h:315 [inline] #3: (&(&tb->tb6_lock)->rlock){+.-.}, at: [<000000009e503581>] __fib6_clean_all+0x1d0/0x3a0 net/ipv6/ip6_fib.c:1948 stack backtrace: CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.15.0-rc5+ #171 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:17 [inline] dump_stack+0x194/0x257 lib/dump_stack.c:53 lockdep_rcu_suspicious+0x123/0x170 kernel/locking/lockdep.c:4585 fib6_del+0xcaa/0x11b0 net/ipv6/ip6_fib.c:1701 fib6_clean_node+0x3aa/0x4f0 net/ipv6/ip6_fib.c:1892 fib6_walk_continue+0x46c/0x8a0 net/ipv6/ip6_fib.c:1815 fib6_walk+0x91/0xf0 net/ipv6/ip6_fib.c:1863 fib6_clean_tree+0x1e6/0x340 net/ipv6/ip6_fib.c:1933 __fib6_clean_all+0x1f4/0x3a0 net/ipv6/ip6_fib.c:1949 fib6_clean_all net/ipv6/ip6_fib.c:1960 [inline] fib6_run_gc+0x16b/0x3c0 net/ipv6/ip6_fib.c:2016 fib6_gc_timer_cb+0x20/0x30 net/ipv6/ip6_fib.c:2033 call_timer_fn+0x228/0x820 kernel/time/timer.c:1320 expire_timers kernel/time/timer.c:1357 [inline] __run_timers+0x7ee/0xb70 kernel/time/timer.c:1660 run_timer_softirq+0x4c/0xb0 kernel/time/timer.c:1686 __do_softirq+0x2d7/0xb85 kernel/softirq.c:285 invoke_softirq kernel/softirq.c:365 [inline] irq_exit+0x1cc/0x200 kernel/softirq.c:405 exiting_irq arch/x86/include/asm/apic.h:540 [inline] smp_apic_timer_interrupt+0x16b/0x700 arch/x86/kernel/apic/apic.c:1052 apic_timer_interrupt+0xa9/0xb0 arch/x86/entry/entry_64.S:904 Reported-by: syzbot Fixes: 66f5d6ce53e6 ("ipv6: replace rwlock with rcu and spinlock in fib6_table") Signed-off-by: Wei Wang Acked-by: Martin KaFai Lau Signed-off-by: David S. Miller --- net/ipv6/ip6_fib.c | 38 +++++++++++++++++++++++++++++--------- 1 file changed, 29 insertions(+), 9 deletions(-) diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c index d11a5578e4f8..9dcc3924a975 100644 --- a/net/ipv6/ip6_fib.c +++ b/net/ipv6/ip6_fib.c @@ -640,6 +640,11 @@ static struct fib6_node *fib6_add_1(struct net *net, if (!(fn->fn_flags & RTN_RTINFO)) { RCU_INIT_POINTER(fn->leaf, NULL); rt6_release(leaf); + /* remove null_entry in the root node */ + } else if (fn->fn_flags & RTN_TL_ROOT && + rcu_access_pointer(fn->leaf) == + net->ipv6.ip6_null_entry) { + RCU_INIT_POINTER(fn->leaf, NULL); } return fn; @@ -1270,13 +1275,17 @@ out: return err; failure: - /* fn->leaf could be NULL if fn is an intermediate node and we - * failed to add the new route to it in both subtree creation - * failure and fib6_add_rt2node() failure case. - * In both cases, fib6_repair_tree() should be called to fix - * fn->leaf. + /* fn->leaf could be NULL and fib6_repair_tree() needs to be called if: + * 1. fn is an intermediate node and we failed to add the new + * route to it in both subtree creation failure and fib6_add_rt2node() + * failure case. + * 2. fn is the root node in the table and we fail to add the first + * default route to it. */ - if (fn && !(fn->fn_flags & (RTN_RTINFO|RTN_ROOT))) + if (fn && + (!(fn->fn_flags & (RTN_RTINFO|RTN_ROOT)) || + (fn->fn_flags & RTN_TL_ROOT && + !rcu_access_pointer(fn->leaf)))) fib6_repair_tree(info->nl_net, table, fn); /* Always release dst as dst->__refcnt is guaranteed * to be taken before entering this function @@ -1531,6 +1540,12 @@ static struct fib6_node *fib6_repair_tree(struct net *net, struct fib6_walker *w; int iter = 0; + /* Set fn->leaf to null_entry for root node. */ + if (fn->fn_flags & RTN_TL_ROOT) { + rcu_assign_pointer(fn->leaf, net->ipv6.ip6_null_entry); + return fn; + } + for (;;) { struct fib6_node *fn_r = rcu_dereference_protected(fn->right, lockdep_is_held(&table->tb6_lock)); @@ -1685,10 +1700,15 @@ static void fib6_del_route(struct fib6_table *table, struct fib6_node *fn, } read_unlock(&net->ipv6.fib6_walker_lock); - /* If it was last route, expunge its radix tree node */ + /* If it was last route, call fib6_repair_tree() to: + * 1. For root node, put back null_entry as how the table was created. + * 2. For other nodes, expunge its radix tree node. + */ if (!rcu_access_pointer(fn->leaf)) { - fn->fn_flags &= ~RTN_RTINFO; - net->ipv6.rt6_stats->fib_route_nodes--; + if (!(fn->fn_flags & RTN_TL_ROOT)) { + fn->fn_flags &= ~RTN_RTINFO; + net->ipv6.rt6_stats->fib_route_nodes--; + } fn = fib6_repair_tree(net, table, fn); } -- 2.30.2