ipv4: Fix NULL pointer dereference in ipv4_neigh_lookup()

Both ip_neigh_gw4() and ip_neigh_gw6() can return either a valid pointer
or an error pointer, but the code currently checks that the pointer is
not NULL.

Fix this by checking that the pointer is not an error pointer, as this
can result in a NULL pointer dereference [1]. Specifically, I believe
that what happened is that ip_neigh_gw4() returned '-EINVAL'
(0xffffffffffffffea) to which the offset of 'refcnt' (0x70) was added,
which resulted in the address 0x000000000000005a.

[1]
 BUG: KASAN: null-ptr-deref in refcount_inc_not_zero_checked+0x6e/0x180
 Read of size 4 at addr 000000000000005a by task swapper/2/0

 CPU: 2 PID: 0 Comm: swapper/2 Not tainted 5.2.0-rc6-custom-reg-179657-gaa32d89 #396
 Hardware name: Mellanox Technologies Ltd. MSN2010/SA002610, BIOS 5.6.5 08/24/2017
 Call Trace:
 <IRQ>
 dump_stack+0x73/0xbb
 __kasan_report+0x188/0x1ea
 kasan_report+0xe/0x20
 refcount_inc_not_zero_checked+0x6e/0x180
 ipv4_neigh_lookup+0x365/0x12c0
 __neigh_update+0x1467/0x22f0
 arp_process.constprop.6+0x82e/0x1f00
 __netif_receive_skb_one_core+0xee/0x170
 process_backlog+0xe3/0x640
 net_rx_action+0x755/0xd90
 __do_softirq+0x29b/0xae7
 irq_exit+0x177/0x1c0
 smp_apic_timer_interrupt+0x164/0x5e0
 apic_timer_interrupt+0xf/0x20
 </IRQ>

Fixes: 5c9f7c1dfc2e ("ipv4: Add helpers for neigh lookup for nexthop")
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Reported-by: Shalom Toledo <shalomt@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 8ea0735a67546b745c2ef5ecd7dd0b5d06a22c77..b2b35b38724d1f993ef62fe6adaa938c66db671e 100644 (file)
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -447,7 +447,7 @@ static struct neighbour *ipv4_neigh_lookup(const struct dst_entry *dst,
                n = ip_neigh_gw4(dev, pkey);
        }
 
-       if (n && !refcount_inc_not_zero(&n->refcnt))
+       if (!IS_ERR(n) && !refcount_inc_not_zero(&n->refcnt))
                n = NULL;
 
        rcu_read_unlock_bh();