netdev - Re: [PATCH net] netlink: fix an use-after-free issue for nlk groups

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Date:   Wed, 06 Sep 2017 21:24:19 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     lucien.xin@...il.com
Cc:     netdev@...r.kernel.org, fw@...len.de, chunwang@...hat.com,
        syzkaller@...glegroups.com
Subject: Re: [PATCH net] netlink: fix an use-after-free issue for nlk groups

From: Xin Long <lucien.xin@...il.com>
Date: Wed,  6 Sep 2017 11:47:12 +0800

> ChunYu found a netlink use-after-free issue by syzkaller:
> 
> [28448.842981] BUG: KASAN: use-after-free in __nla_put+0x37/0x40 at addr ffff8807185e2378
> [28448.969918] Call Trace:
> [...]
> [28449.117207]  __nla_put+0x37/0x40
> [28449.132027]  nla_put+0xf5/0x130
> [28449.146261]  sk_diag_fill.isra.4.constprop.5+0x5a0/0x750 [netlink_diag]
> [28449.176608]  __netlink_diag_dump+0x25a/0x700 [netlink_diag]
> [28449.202215]  netlink_diag_dump+0x176/0x240 [netlink_diag]
> [28449.226834]  netlink_dump+0x488/0xbb0
> [28449.298014]  __netlink_dump_start+0x4e8/0x760
> [28449.317924]  netlink_diag_handler_dump+0x261/0x340 [netlink_diag]
> [28449.413414]  sock_diag_rcv_msg+0x207/0x390
> [28449.432409]  netlink_rcv_skb+0x149/0x380
> [28449.467647]  sock_diag_rcv+0x2d/0x40
> [28449.484362]  netlink_unicast+0x562/0x7b0
> [28449.564790]  netlink_sendmsg+0xaa8/0xe60
> [28449.661510]  sock_sendmsg+0xcf/0x110
> [28449.865631]  __sys_sendmsg+0xf3/0x240
> [28450.000964]  SyS_sendmsg+0x32/0x50
> [28450.016969]  do_syscall_64+0x25c/0x6c0
> [28450.154439]  entry_SYSCALL64_slow_path+0x25/0x25
> 
> It was caused by no protection between nlk groups' free in netlink_release
> and nlk groups' accessing in sk_diag_dump_groups. The similar issue also
> exists in netlink_seq_show().
> 
> This patch is to defer nlk groups' free in deferred_put_nlk_sk.
> 
> Reported-by: ChunYu Wang <chunwang@...hat.com>
> Acked-by: Florian Westphal <fw@...len.de>
> Signed-off-by: Xin Long <lucien.xin@...il.com>

Applied.