4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Wolfgang Bumiller <w.bumiller@xxxxxxxxxxx> [ Upstream commit 53b76cdf7e8fecec1d09e38aad2f8579882591a8 ] 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@xxxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/core/neighbour.c | 28 ++++++++++++++++++---------- 1 file changed, 18 insertions(+), 10 deletions(-) --- 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); #ifdef CONFIG_PROC_FS static const struct file_operations neigh_stat_seq_fops; @@ -254,8 +255,7 @@ 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); @@ -645,9 +645,10 @@ 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++) { @@ -655,16 +656,23 @@ 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); - 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); + kfree(n); + } return -ENOENT; }