mount.cifs stopped working with protocol version>1 and sec=ntlm

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apport-collect 1746482

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This change has been made by an automated script, maintained by the Ubuntu Kernel Team.

As discussed with cascardo I tested the mainline builds from [1].

After some tests the results were:
v4.12.14 - good
v4.13 - bad

So the regression seems to be introduced in v4.13.

[1] http://kernel.ubuntu.com/~kernel-ppa/mainline/

dmesg output after reproducing the issue with
echo 7 > /proc/fs/cifs/cifsFYI

Can you see if this bug has been fixed in the latest mainline kernel:
http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.15/

If the bug still exists in 4.15, we can bisect between 4.12 and 4.13.

Surprisingly it works perfectly fine for 4.15.0-041500-generic.

I have tested vers= parameter from 1.0 to 3.0 - no issues at all.

I went forward and tested v4.14 - it is not affected by the issue as well.

Looks like I've been mislead by the man page of mount.cifs and linux/fs/cifs/connect.c which state:

man mount.cifs:
vers=
           SMB protocol version. Allowed values are:

           · 1.0 - The classic CIFS/SMBv1 protocol. This is the default.

4.13 kernel code:
pr_warn("No dialect specified on mount. Default has changed to "
                        "a more secure dialect, SMB2.1 or later (e.g. SMB3), from CIFS "
                        "(SMB1). To use the less secure SMB1 dialect to access "
                        "old servers which do not support SMB3 (or SMB2.1) specify vers=1.0"
                        " on mount.\n");

So looks like I need to explicitly apply the version number to mount.cifs argument to have consistent results.

More over sec=ntlm is needed in smb.conf and mount.cifs cmdline.

Updating the description.

Added updated dmesg (with verbose error message).

Conclusion after correcting the parameters in my test procedure:
v4.10 - good
v4.11 - bad
v4.15 - bad

I'm performing a bisect between v4.10 and v4.11.

Bisecting between v4.10 and v4.11 resulted in finding that this was caused by the following commit:
[ef65aaede23f75977af56a8c330bb9be8c6e125c] smb2: Enforce sec= mount option

Reverting it on top of v4.11 makes it go away.

Looking more into it.

After the preliminary analysis my understanding is as follows:
since the change found thanks to the bisection the behaviour change in a way that if an unsupported security mode is requested it results in an error (invalid argument in this case).

Looks like NTLM was not supported even before the change in question, it was just unnoticed since it was silently mapped to NTLMSSP.

So no actual regression in functionality is observed, but rather regression in UI being less restrictive before the kernel change.

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