linux-kernel - Re: [PATCH] cifs: Fix getting reparse points from server without WSL support

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Message-ID: <20240917200600.6smfxhrppkyjuyku@pali>
Date: Tue, 17 Sep 2024 22:06:00 +0200
From: Pali Rohár <pali@...nel.org>
To: Steve French <sfrench@...ba.org>, Paulo Alcantara <pc@...guebit.com>
Cc: linux-cifs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cifs: Fix getting reparse points from server without WSL
 support

And seems that SMB2_OP_QUERY_WSL_EA is useful not only for reparse
points, but also for any regular file or directory as it can contain
UNIX mode and UID/GID ownership.

On Friday 13 September 2024 22:10:41 Pali Rohár wrote:
> Paulo, please look at this patch as it is related to WSL attributes
> which you introduced in the mentioned commit. I think that the proper
> fix should be to change SMB2_OP_QUERY_WSL_EA code to not trigger that
> -EOPNOTSUPP error which is delivered to userspace. I just checked that
> this my patch works fine for Native NTFS symlinks and NFS-style reparse
> point special files.
> 
> On Friday 13 September 2024 22:02:04 Pali Rohár wrote:
> > If SMB server does not support WSL EAs then for SMB2_OP_QUERY_WSL_EA
> > request it returns STATUS_EAS_NOT_SUPPORTED. Function smb2_compound_op()
> > translates STATUS_EAS_NOT_SUPPORTED to -EOPNOTSUPP which cause failure
> > during calling lstat() syscall from userspace on any reparse point,
> > including Native SMB symlink (which does not use any EAs). This issue
> > happen for example when trying to resolve Native NTFS symlink from SMB
> > server on Windows 8.
> > 
> > Avoid this problem by calling SMB2_OP_QUERY_WSL_EA only when detected
> > reparse point is of WSL type. Note that this is not solve this problem
> > fully as WSL reparse points can be created also on other SMB server
> > which do not support Extended Attributes at all.
> > 
> > Fixes: ea41367b2a60 ("smb: client: introduce SMB2_OP_QUERY_WSL_EA")
> > Signed-off-by: Pali Rohár <pali@...nel.org>
> > ---
> >  fs/smb/client/smb2inode.c | 15 ++++++++++++++-
> >  1 file changed, 14 insertions(+), 1 deletion(-)
> > 
> > diff --git a/fs/smb/client/smb2inode.c b/fs/smb/client/smb2inode.c
> > index 11a1c53c64e0..d65471aa55e6 100644
> > --- a/fs/smb/client/smb2inode.c
> > +++ b/fs/smb/client/smb2inode.c
> > @@ -941,7 +941,20 @@ int smb2_query_path_info(const unsigned int xid,
> >  		if (rc || !data->reparse_point)
> >  			goto out;
> >  
> > -		cmds[num_cmds++] = SMB2_OP_QUERY_WSL_EA;
> > +		/*
> > +		 * Skip SMB2_OP_QUERY_WSL_EA if reparse point is not WSL.
> > +		 * The server file system does not have to support Extended
> > +		 * Attributes and in this case returns STATUS_EAS_NOT_SUPPORTED
> > +		 * which smb2_compound_op() translate to -EOPNOTSUPP. This will
> > +		 * present failure during reading of non-WSL special files.
> > +		 */
> > +		if (data->reparse.tag == IO_REPARSE_TAG_LX_SYMLINK ||
> > +		    data->reparse.tag == IO_REPARSE_TAG_AF_UNIX ||
> > +		    data->reparse.tag == IO_REPARSE_TAG_LX_FIFO ||
> > +		    data->reparse.tag == IO_REPARSE_TAG_LX_CHR ||
> > +		    data->reparse.tag == IO_REPARSE_TAG_LX_BLK)
> > +			cmds[num_cmds++] = SMB2_OP_QUERY_WSL_EA;
> > +
> >  		/*
> >  		 * Skip SMB2_OP_GET_REPARSE if symlink already parsed in create
> >  		 * response.
> > -- 
> > 2.20.1
> >