Re: [PATCH v4] ksmbd: fix invalid request buffer access in compound

[Namjae Jeon <linkinjeon@kernel.org>]

2021-09-24 0:13 GMT+09:00, Tom Talpey <tom@talpey.com>:
> On 9/22/2021 11:48 PM, Namjae Jeon wrote:
>> Ronnie reported invalid request buffer access in chained command when
>> inserting garbage value to NextCommand of compound request.
>> This patch add validation check to avoid this issue.
>>
>> Cc: Tom Talpey <tom@talpey.com>
>> Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
>> Cc: Ralph Böhme <slow@samba.org>
>> Cc: Steve French <smfrench@gmail.com>
>> Reported-by: Ronnie Sahlberg <lsahlber@redhat.com>
>> Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
>> ---
>>    v2:
>>     - fix integer overflow from work->next_smb2_rcv_hdr_off.
>>    v3:
>>     - check next command offset and at least header size of next pdu at
>>       the same time.
>>    v4:
>>     - add next_cmd variable not to avoid repeat conversion.
>>
>>   fs/ksmbd/smb2pdu.c | 12 ++++++++++--
>>   1 file changed, 10 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/ksmbd/smb2pdu.c b/fs/ksmbd/smb2pdu.c
>> index 90f867b9d560..301558a04298 100644
>> --- a/fs/ksmbd/smb2pdu.c
>> +++ b/fs/ksmbd/smb2pdu.c
>> @@ -459,13 +459,21 @@ static void init_chained_smb2_rsp(struct ksmbd_work
>> *work)
>>   bool is_chained_smb2_message(struct ksmbd_work *work)
>>   {
>>   	struct smb2_hdr *hdr = work->request_buf;
>> -	unsigned int len;
>> +	unsigned int len, next_cmd;
>>
>>   	if (hdr->ProtocolId != SMB2_PROTO_NUMBER)
>>   		return false;
>>
>>   	hdr = ksmbd_req_buf_next(work);
>> -	if (le32_to_cpu(hdr->NextCommand) > 0) {
>> +	next_cmd = le32_to_cpu(hdr->NextCommand);
>> +	if (next_cmd > 0) {
>> +		if ((u64)work->next_smb2_rcv_hdr_off + next_cmd + 64 >
>
> The "64" is somewhat arbitrary and mysterious. Is this the size
> of the next command smb2_hdr? Why not code that, at least with
> a #define?
Okay, Will use macro.
>
>> +		    get_rfc1002_len(work->request_buf)) {
>> +			pr_err("next command(%u) offset exceeds smb msg size\n",
>> +			       next_cmd);
>> +			return false;
>> +		}
>
> Hmm, well the header fits in the reminder of the message. What
> about the rest of the nextcommand smb2 request? It seems very
> odd, and more than a little risky, to be validating only one
> aspect of the nextcommand here.
There is a loop to check the rest of the nextcommand.
Please see do { } while (is_chained_smb2_message(work)); in server.

>
>> +
>>   		ksmbd_debug(SMB, "got SMB2 chained command\n");
>
> This, to me, is entirely needless debug splat.
The reason is ?
>
> Tom.
>
>>   		init_chained_smb2_rsp(work);
>>   		return true;
>>
>