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Message-ID: <CAM_iQpU_ve5fRGeYmBFfYc5DgDPk0sngku=3y1dOc8py4PDAfw@mail.gmail.com>
Date: Fri, 8 Sep 2017 14:56:36 -0700
From: Cong Wang <xiyou.wangcong@...il.com>
To: Xin Long <lucien.xin@...il.com>
Cc: network dev <netdev@...r.kernel.org>,
David Miller <davem@...emloft.net>,
Florian Westphal <fw@...len.de>, chunwang@...hat.com,
syzkaller <syzkaller@...glegroups.com>
Subject: Re: [PATCH net] netlink: fix an use-after-free issue for nlk groups
On Tue, Sep 5, 2017 at 8:47 PM, Xin Long <lucien.xin@...il.com> wrote:
> 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.
This looks odd too, at least not complete.
The netlink sock itself is protected by RCU to speed up
the lookup path, but not necessarily nlk->groups, at least
I don't see rcu_dereference() in sk_diag_dump_groups().
And netlink_realloc_groups() needs fix too, right? Otherwise
krealloc() could reallocate a brand new memory and
existing readers will crash too?
I am afraid you need more work to make nlk->groups
RCU friendly. RCU is not just about call_rcu(), both
readers and writers need to use proper RCU API.
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