From: Wei Wang <wei...@google.com>
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:
<IRQ>
__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
</IRQ>
Reported-by: syzbot <syzkal...@googlegroups.com>
Fixes: 66f5d6ce53e6 ("ipv6: replace rwlock with rcu and spinlock in fib6_table")
Signed-off-by: Wei Wang <wei...@google.com>
---
net/ipv6/ip6_fib.c | 45 +++++++++++++++++++++++++++++++++++----------
1 file changed, 35 insertions(+), 10 deletions(-)
diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index d11a5578e4f8..37cb4ad1ea29 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;
@@ -1270,14 +1275,27 @@ int fib6_add(struct fib6_node *root, struct rt6_info
*rt,
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 could be NULL if:
+ * 1. fn is the root node in the table and we fail to add the default
+ * route to it.
+ * In this case, we put fn->leaf back to net->ipv6.ip6_null_entry as
+ * the way the table was created.
+ * 2. 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 this case, fib6_repair_tree() should be called to fix
* fn->leaf.
*/
- if (fn && !(fn->fn_flags & (RTN_RTINFO|RTN_ROOT)))
- fib6_repair_tree(info->nl_net, table, fn);
+ if (fn) {
+ if (fn->fn_flags & RTN_TL_ROOT) {
+ if (!rcu_access_pointer(fn->leaf)) {
+ rcu_assign_pointer(fn->leaf,
+ info->nl_net->ipv6.ip6_null_entry);
+ }
+ } else if (!(fn->fn_flags & (RTN_RTINFO|RTN_ROOT))) {
+ fib6_repair_tree(info->nl_net, table, fn);
+ }
+ }
/* Always release dst as dst->__refcnt is guaranteed
* to be taken before entering this function
*/
@@ -1685,11 +1703,18 @@ 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:
+ * 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--;
- fn = fib6_repair_tree(net, table, fn);
+ if (fn->fn_flags & RTN_TL_ROOT) {
+ rcu_assign_pointer(fn->leaf, net->ipv6.ip6_null_entry);
+ } else {
+ fn->fn_flags &= ~RTN_RTINFO;
+ net->ipv6.rt6_stats->fib_route_nodes--;
+ fn = fib6_repair_tree(net, table, fn);
+ }
}
fib6_purge_rt(rt, fn, net);
--
2.16.0.rc0.223.g4a4ac83678-goog
