[PATCH 3.16 144/366] net: fix deadlock while clearing neighbor proxy table

Ben Hutchings
2018-10-14T23:28:38Z

From: Wolfgang Bumiller <w.bumiller@proxmox.com>

commit 53b76cdf7e8fecec1d09e38aad2f8579882591a8 upstream.

When coming from ndisc_netdev_event() in net/ipv6/ndisc.c,
neigh_ifdown() is called with &nd_tbl, locking this while
clearing the proxy neighbor entries when eg. deleting an
interface. Calling the table's pndisc_destructor() with the
lock still held, however, can cause a deadlock: When a
multicast listener is available an IGMP packet of type
ICMPV6_MGM_REDUCTION may be sent out. When reaching
ip6_finish_output2(), if no neighbor entry for the target
address is found, __neigh_create() is called with &nd_tbl,
which it'll want to lock.

Move the elements into their own list, then unlock the table
and perform the destruction.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=199289
Fixes: 6fd6ce2056de ("ipv6: Do not depend on rt->n in ip6_finish_output2().")
Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.16:
- Move the (useless) call to release_net() as well
- Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -54,7 +54,8 @@ do { \
static void neigh_timer_handler(unsigned long arg);
static void __neigh_notify(struct neighbour *n, int type, int flags);
static void neigh_update_notify(struct neighbour *neigh);
-static int pneigh_ifdown(struct neigh_table *tbl, struct net_device *dev);
+static int pneigh_ifdown_and_unlock(struct neigh_table *tbl,
+ struct net_device *dev);

static struct neigh_table *neigh_tables;
#ifdef CONFIG_PROC_FS
@@ -260,8 +261,7 @@ int neigh_ifdown(struct neigh_table *tbl
{
write_lock_bh(&tbl->lock);
neigh_flush_dev(tbl, dev);
- pneigh_ifdown(tbl, dev);
- write_unlock_bh(&tbl->lock);
+ pneigh_ifdown_and_unlock(tbl, dev);

del_timer_sync(&tbl->proxy_timer);
pneigh_queue_purge(&tbl->proxy_queue);
@@ -659,9 +659,10 @@ int pneigh_delete(struct neigh_table *tb
return -ENOENT;
}

-static int pneigh_ifdown(struct neigh_table *tbl, struct net_device *dev)
+static int pneigh_ifdown_and_unlock(struct neigh_table *tbl,
+ struct net_device *dev)
{
- struct pneigh_entry *n, **np;
+ struct pneigh_entry *n, **np, *freelist = NULL;
u32 h;

for (h = 0; h <= PNEIGH_HASHMASK; h++) {
@@ -669,17 +670,24 @@ static int pneigh_ifdown(struct neigh_ta
while ((n = *np) != NULL) {
if (!dev || n->dev == dev) {
*np = n->next;
- if (tbl->pdestructor)
- tbl->pdestructor(n);
- if (n->dev)
- dev_put(n->dev);
- release_net(pneigh_net(n));
- kfree(n);
+ n->next = freelist;
+ freelist = n;
continue;
}
np = &n->next;
}
}
+ write_unlock_bh(&tbl->lock);
+ while ((n = freelist)) {
+ freelist = n->next;
+ n->next = NULL;
+ if (tbl->pdestructor)
+ tbl->pdestructor(n);
+ if (n->dev)
+ dev_put(n->dev);
+ release_net(pneigh_net(n));
+ kfree(n);
+ }
return -ENOENT;
}