linux-kernel - Re: [PATCH 0/2] cifs: Improve access without FILE_READ

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Message-ID: <20241005184453.rdxetlsoszxzfqnt@pali>
Date: Sat, 5 Oct 2024 20:44:53 +0200
From: Pali Rohár <pali@...nel.org>
To: Steve French <smfrench@...il.com>
Cc: Steve French <sfrench@...ba.org>, Paulo Alcantara <pc@...guebit.com>,
	Ronnie Sahlberg <ronniesahlberg@...il.com>,
	linux-cifs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] cifs: Improve access without FILE_READ_ATTRIBUTES
 permission

On Saturday 05 October 2024 13:32:12 Steve French wrote:
> The obvious question to check is whether this would lead to any issues
> if desired_access is not passed in in oparms in any cases (ie if it
> ends up 0),

This is good point. IIRC if zero value is in OPEN/CREATE desired_access
request then SMB server returns STATUS_ACCESS_DENIED.

So it needs to be checked that desired_access is filled in all usage
correctly.

> and also that this would not hurt any cases where we want
> to keep the handle cached (deferred close) but don't have sufficient
> permission for it to be usable by the subsequent operation (e.g.
> revalidate or stat)

I see, so the code needs to be properly checked or tested that all these
conditions are handled.

> On Sat, Oct 5, 2024 at 11:10 AM Pali Rohár <pali@...nel.org> wrote:
> >
> > Linux SMB client currently is not able to access files for which do not
> > have FILE_READ_ATTRIBUTES permission.
> >
> > For example it is not able to write data into file on SMB server to
> > which has only write access (no read or read attributes access). And
> > applications are not able to get result of stat() syscall on such file.
> >
> > Test case against Windows SMB server:
> >
> > 1) On SMB server prepare file with only GENERIC_WRITE access for Everyone:
> >    ACL:S-1-1-0:ALLOWED/0x0/0x40000000
> >
> > 2) On SMB server remove all access for file's parent directory
> >
> > 3) Mount share by Linux SMB client and try to append data to that file:
> >    echo test >> /mnt/share/dir/file
> >
> > 4) Try to call: stat /mnt/share/dir/file
> >
> > Without this change the write test fails because Linux SMB client is trying
> > to open SMB path "\dir\file" with GENERIC_WRITE|FILE_READ_ATTRIBUTES. With
> > this change the test pass as Linux SMB client is not opening file with
> > FILE_READ_ATTRIBUTES access anymore.
> >
> > Similarly without this change the stat test always fails as Linux SMB
> > client is trying to read attributes via SMB2_OP_QUERY_INFO. With this
> > change, if SMB2_OP_QUERY_INFO fails then Linux SMB client fallbacks for
> > reading stat attributes via OPEN with MAXIMUM_ALLOWED access (which will
> > pass if there is some permission) and OPEN reply will contain attributes
> > required for stat().
> >
> > Pali Rohár (2):
> >   cifs: Do not issue SMB2 CREATE always with FILE_READ_ATTRIBUTES
> >   cifs: Improve stat() to work also without FILE_READ_ATTRIBUTES
> >
> >  fs/smb/client/cifspdu.h   |  1 +
> >  fs/smb/client/smb2file.c  |  1 -
> >  fs/smb/client/smb2glob.h  |  1 +
> >  fs/smb/client/smb2inode.c | 71 ++++++++++++++++++++++++++++++++++++++-
> >  4 files changed, 72 insertions(+), 2 deletions(-)
> >
> > --
> > 2.20.1
> >
> >
> 
> 
> -- 
> Thanks,
> 
> Steve