Re: [PATCH][SMB3.1.1] remove confusing mount warning when no SPNEGO info on negprot rsp

[Tom Talpey <tom@talpey.com>]

The protocol allows omitting the SPNEGO blob altogether, btw. That
leads to the client deciding how to authenticate, although the Windows
server doesn't offer that.

So I'd suggest removing the comment, too:

 >> /* Make sure that negotiate contexts start after gss security blob */


On 12/9/2020 12:39 PM, Pavel Shilovsky wrote:
> Looks good.
> 
> Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
> 
> --
> Best regards,
> Pavel Shilovsky
> 
> вт, 8 дек. 2020 г. в 23:23, Steve French <smfrench@gmail.com>:
>>
>> Azure does not send an SPNEGO blob in the negotiate protocol response,
>> so we shouldn't assume that it is there when validating the location
>> of the first negotiate context.  This avoids the potential confusing
>> mount warning:
>>
>>     CIFS: Invalid negotiate context offset
>>
>> CC: Stable <stable@vger.kernel.org>
>> Signed-off-by: Steve French <stfrench@microsoft.com>
>> ---
>>   fs/cifs/smb2misc.c | 11 +++++++----
>>   1 file changed, 7 insertions(+), 4 deletions(-)
>>
>> diff --git a/fs/cifs/smb2misc.c b/fs/cifs/smb2misc.c
>> index d88e2683626e..513507e4c4ad 100644
>> --- a/fs/cifs/smb2misc.c
>> +++ b/fs/cifs/smb2misc.c
>> @@ -109,11 +109,14 @@ static __u32 get_neg_ctxt_len(struct
>> smb2_sync_hdr *hdr, __u32 len,
>>
>>    /* Make sure that negotiate contexts start after gss security blob */
>>    nc_offset = le32_to_cpu(pneg_rsp->NegotiateContextOffset);
>> - if (nc_offset < non_ctxlen) {
>> - pr_warn_once("Invalid negotiate context offset\n");
>> + if (nc_offset + 1 < non_ctxlen) {
>> + pr_warn_once("Invalid negotiate context offset %d\n", nc_offset);
>>    return 0;
>> - }
>> - size_of_pad_before_neg_ctxts = nc_offset - non_ctxlen;
>> + } else if (nc_offset + 1 == non_ctxlen) {
>> + cifs_dbg(FYI, "no SPNEGO security blob in negprot rsp\n");
>> + size_of_pad_before_neg_ctxts = 0;
>> + } else
>> + size_of_pad_before_neg_ctxts = nc_offset - non_ctxlen;
>>
>>    /* Verify that at least minimal negotiate contexts fit within frame */
>>    if (len < nc_offset + (neg_count * sizeof(struct smb2_neg_context))) {
>>
>> --
>> Thanks,
>>
>> Steve
>