Patch "net, neigh: Fix null-ptr-deref in neigh_table_clear()" has been added to the 4.14-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    net, neigh: Fix null-ptr-deref in neigh_table_clear()

to the 4.14-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     net-neigh-fix-null-ptr-deref-in-neigh_table_clear.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 8d99f8456ba61cdd7d2d0b616384a8fe144f6eb8
Author: Chen Zhongjin <chenzhongjin@xxxxxxxxxx>
Date:   Tue Nov 1 20:15:52 2022 +0800

    net, neigh: Fix null-ptr-deref in neigh_table_clear()
    
    [ Upstream commit f8017317cb0b279b8ab98b0f3901a2e0ac880dad ]
    
    When IPv6 module gets initialized but hits an error in the middle,
    kenel panic with:
    
    KASAN: null-ptr-deref in range [0x0000000000000598-0x000000000000059f]
    CPU: 1 PID: 361 Comm: insmod
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
    RIP: 0010:__neigh_ifdown.isra.0+0x24b/0x370
    RSP: 0018:ffff888012677908 EFLAGS: 00000202
    ...
    Call Trace:
     <TASK>
     neigh_table_clear+0x94/0x2d0
     ndisc_cleanup+0x27/0x40 [ipv6]
     inet6_init+0x21c/0x2cb [ipv6]
     do_one_initcall+0xd3/0x4d0
     do_init_module+0x1ae/0x670
    ...
    Kernel panic - not syncing: Fatal exception
    
    When ipv6 initialization fails, it will try to cleanup and calls:
    
    neigh_table_clear()
      neigh_ifdown(tbl, NULL)
        pneigh_queue_purge(&tbl->proxy_queue, dev_net(dev == NULL))
        # dev_net(NULL) triggers null-ptr-deref.
    
    Fix it by passing NULL to pneigh_queue_purge() in neigh_ifdown() if dev
    is NULL, to make kernel not panic immediately.
    
    Fixes: 66ba215cb513 ("neigh: fix possible DoS due to net iface start/stop loop")
    Signed-off-by: Chen Zhongjin <chenzhongjin@xxxxxxxxxx>
    Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
    Reviewed-by: Denis V. Lunev <den@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20221101121552.21890-1-chenzhongjin@xxxxxxxxxx
    Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 51aacfdd4fb7..8e71f392ce21 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -310,7 +310,7 @@ int neigh_ifdown(struct neigh_table *tbl, struct net_device *dev)
 	write_lock_bh(&tbl->lock);
 	neigh_flush_dev(tbl, dev);
 	pneigh_ifdown_and_unlock(tbl, dev);
-	pneigh_queue_purge(&tbl->proxy_queue, dev_net(dev));
+	pneigh_queue_purge(&tbl->proxy_queue, dev ? dev_net(dev) : NULL);
 	if (skb_queue_empty_lockless(&tbl->proxy_queue))
 		del_timer_sync(&tbl->proxy_timer);
 	return 0;