Re: [PATCH] xfrm/compat: Fix general protection fault in xfrm_user_rcv_msg_compat()

[Dmitry Safonov <dima@arista.com>]

On 7/16/21 9:01 AM, Steffen Klassert wrote:
> On Mon, Jul 12, 2021 at 09:40:02PM +0800, YueHaibing wrote:
>> In xfrm_user_rcv_msg_compat() if maxtype is not zero and less than
>> XFRMA_MAX, nlmsg_parse_deprecated() do not initialize attrs array fully.
>> xfrm_xlate32() will access uninit 'attrs[i]' while iterating all attrs
>> array.
>>
>> KASAN: probably user-memory-access in range [0x0000000041b58ab0-0x0000000041b58ab7]
>> CPU: 0 PID: 15799 Comm: syz-executor.2 Tainted: G        W         5.14.0-rc1-syzkaller #0
>> RIP: 0010:nla_type include/net/netlink.h:1130 [inline]
>> RIP: 0010:xfrm_xlate32_attr net/xfrm/xfrm_compat.c:410 [inline]
>> RIP: 0010:xfrm_xlate32 net/xfrm/xfrm_compat.c:532 [inline]
>> RIP: 0010:xfrm_user_rcv_msg_compat+0x5e5/0x1070 net/xfrm/xfrm_compat.c:577
>> [...]
>> Call Trace:
>>  xfrm_user_rcv_msg+0x556/0x8b0 net/xfrm/xfrm_user.c:2774
>>  netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2504
>>  xfrm_netlink_rcv+0x6b/0x90 net/xfrm/xfrm_user.c:2824
>>  netlink_unicast_kernel net/netlink/af_netlink.c:1314 [inline]
>>  netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1340
>>  netlink_sendmsg+0x86d/0xdb0 net/netlink/af_netlink.c:1929
>>  sock_sendmsg_nosec net/socket.c:702 [inline]
>>
>> Fixes: 5106f4a8acff ("xfrm/compat: Add 32=>64-bit messages translator")
>> Signed-off-by: YueHaibing <yuehaibing@huawei.com>
>> ---
>>  net/xfrm/xfrm_compat.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/xfrm/xfrm_compat.c b/net/xfrm/xfrm_compat.c
>> index a20aec9d7393..4738660cadea 100644
>> --- a/net/xfrm/xfrm_compat.c
>> +++ b/net/xfrm/xfrm_compat.c
>> @@ -559,8 +559,8 @@ static struct nlmsghdr *xfrm_user_rcv_msg_compat(const struct nlmsghdr *h32,
>>  	    (h32->nlmsg_flags & NLM_F_DUMP))
>>  		return NULL;
>>  
>> -	err = nlmsg_parse_deprecated(h32, compat_msg_min[type], attrs,
>> -			maxtype ? : XFRMA_MAX, policy ? : compat_policy, extack);
>> +	err = nlmsg_parse_deprecated(h32, compat_msg_min[type], attrs, XFRMA_MAX,
>> +				     policy ? : compat_policy, extack);
> 
> This removes the only usage of maxtype in that function. If we don't
> need it, we should remove maxtype from the function parameters.
> 
> But looking closer at this, it seems that xfrm_xlate32() should
> only iterate up to maxtype if set. Dimitry, any opinion on that?
> 

Thanks for Cc. Yeah, I agree, it should pass maxtype to xfrm_xlate32().
More than that, it is XFRM_MSG_NEWSPDINFO, which have different possible
attributes: XFRMA_SPD_MAX vs XFRMA_MAX, so attribute translator
xfrm_xlate32_attr() should be corrected to translate these.

Let me fix this, thanks for the report!
I'll also add a selftest for this to xfrm selftest.

Thanks,
          Dmitry