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net: fix deadlock while clearing neighbor proxy table 

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: 6fd6ce2056 ("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>
This commit is contained in:
Wolfgang Bumiller 2018-04-12 10:46:55 +02:00 committed by syphyr
parent ae2f43d389
commit 2b61b2cb8e
1 changed files with 19 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

30
net/core/neighbour.c
View File

@ -52,7 +52,8 @@ 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;
static unsigned neigh_probe_enable;
@ -259,8 +260,7 @@ int neigh_ifdown(struct neigh_table *tbl, struct net_device *dev)
{
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);
@ -658,9 +658,10 @@ int pneigh_delete(struct neigh_table *tbl, struct net *net, const void *pkey,
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++) {
@ -668,17 +669,24 @@ static int pneigh_ifdown(struct neigh_table *tbl, struct net_device *dev)
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;
}