Re: [PATCH 0/2] cifs: Improve access without FILE_READ_ATTRIBUTES permission

[Steve French]

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), 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)

On Sat, Oct 5, 2024 at 11:10 AM Pali Rohár <pali@xxxxxxxxxx> 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