Re: net/netlink: global-out-of-bounds in genl_family_rcv_msg/validate_nla

[Cong Wang]

On Wed, Nov 2, 2016 at 10:25 PM, Cong Wang <xiyou.wangcong@xxxxxxxxx> wrote:
> On Wed, Nov 2, 2016 at 5:25 PM, Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote:
>> Hi,
>>
>> I've got the following error report while running the syzkaller fuzzer:
>>
>> ==================================================================
>> BUG: KASAN: global-out-of-bounds in validate_nla+0x49b/0x4e0 at addr
>> ffffffff8407e3ac
>> Read of size 2 by task a.out/3877
>> Address belongs to variable[<        none        >]
>> cgroupstats_cmd_get_policy+0xc/0x40 ??:?
>
> Seems taskstats doesn't use genetlink correctly, CGROUPSTATS_CMD_ATTR_FD
> is not within 0~TASKSTATS_CMD_ATTR_MAX.
>
> I guess we need the following patch, but it certainly breaks user-space... :-/


Wait, maybe just this one-line fix is enough:

diff --git a/kernel/taskstats.c b/kernel/taskstats.c
index b3f05ee..e6b342e 100644
--- a/kernel/taskstats.c
+++ b/kernel/taskstats.c
@@ -54,7 +54,7 @@ static const struct nla_policy
taskstats_cmd_get_policy[TASKSTATS_CMD_ATTR_MAX+1
        [TASKSTATS_CMD_ATTR_REGISTER_CPUMASK] = { .type = NLA_STRING },
        [TASKSTATS_CMD_ATTR_DEREGISTER_CPUMASK] = { .type = NLA_STRING },};

-static const struct nla_policy
cgroupstats_cmd_get_policy[CGROUPSTATS_CMD_ATTR_MAX+1] = {
+static const struct nla_policy
cgroupstats_cmd_get_policy[TASKSTATS_CMD_ATTR_MAX+1] = {
        [CGROUPSTATS_CMD_ATTR_FD] = { .type = NLA_U32 },
 };