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List:       wine-devel
Subject:    Re: [PATCH v2 0/8] Add O_DENY* support for VFS and CIFS/NFS
From:       "J. Bruce Fields" <bfields () fieldses ! org>
Date:       2013-01-30 22:11:18
Message-ID: 20130130221118.GB15584 () fieldses ! org
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On Thu, Jan 17, 2013 at 08:52:09PM +0400, Pavel Shilovsky wrote:
> This patchset adds support of O_DENY* flags for Linux fs layer. These flags can be \
> used by any application that needs share reservations to organize a file access. \
> VFS already has some sort of this capability - now it's done through \
> flock/LOCK_MAND mechanis, but that approach is non-atomic. This patchset build new \
> capabilities on top of the existing one but doesn't bring any changes into the \
> flock call semantic. 
> These flags can be used by NFS (built-in-kernel) and CIFS (Samba) servers and Wine \
> applications through VFS (for local filesystems) or CIFS/NFS modules. This will \
> help when e.g. Samba and NFS server share the same directory for Windows and Linux \
> users or Wine applications use Samba/NFS share to access the same data from \
> different clients. 
> According to the previous discussions the most problematic question is how to \
> prevent situations like DoS attacks where e.g /lib/liba.so file can be open with \
> DENYREAD, or smth like this. That's why one extra flag O_DENYMAND is added. It \
> indicates to underlying layer that an application want to use O_DENY* flags \
> semantic. It allows us not affect native Linux applications (that don't use \
> O_DENYMAND flag) - so, these flags (and the semantic of open syscall that they \
> bring) are used only for those applications that really want it proccessed that \
> way.

Maybe that's good enough.  A mount flag might be simpler and give
consistent enforcement for all users.

> 
> So, we have four new flags:
> O_DENYREAD - to prevent other opens with read access,
> O_DENYWRITE - to prevent other opens with write access,
> O_DENYDELETE - to prevent delete operations (this flag is not implemented in VFS \
> and NFS part and only suitable for CIFS module), O_DENYMAND - to switch on/off \
> three flags above.

It would be useful to have some really careful documentation of how
these are meant to work.  Maybe try updating the open man page?

--b.
> 
> The #1 patch bring infrastructure to let us add this capability easier. #2 patch \
> adds flags to fcntl while #3 patch implement VFS part. Patches #4, #5, #6 are \
> related to CIFS-specific changes. #7 and #8 describe NFS and NFSD parts. 
> Also, I created the preliminary patch for Samba that replaces the existing use of \
> flock/LOCK_MAND mechanism with O_DENY* flags: \
> http://git.etersoft.ru/people/piastry/packages/?p=samba.git;a=commitdiff;h=f116c478bf9a1bc3985e9a719fb20d854914d67a
>  
> Pavel Shilovsky (8):
> locks: make flock_lock_file take is_conflict callback parm
> fcntl: Introduce new O_DENY* open flags
> vfs: Add O_DENYREAD/WRITE flags support for open syscall
> CIFS: Add O_DENY* open flags support
> CIFS: Use NT_CREATE_ANDX command for forcemand mounts
> CIFS: Translate SHARING_VIOLATION to -ETXTBSY error code for SMB2
> NFSv4: Add O_DENY* open flags support
> NFSD: Pass share reservations flags to VFS
> 
> fs/cifs/cifsacl.c                |  10 ++--
> fs/cifs/cifsglob.h               |  12 +++-
> fs/cifs/cifsproto.h              |   9 +--
> fs/cifs/cifssmb.c                |  47 ++++++++-------
> fs/cifs/dir.c                    |  14 +++--
> fs/cifs/file.c                   |  18 ++++--
> fs/cifs/inode.c                  |  11 ++--
> fs/cifs/link.c                   |  10 ++--
> fs/cifs/readdir.c                |   2 +-
> fs/cifs/smb1ops.c                |  15 ++---
> fs/cifs/smb2file.c               |  10 ++--
> fs/cifs/smb2inode.c              |   4 +-
> fs/cifs/smb2maperror.c           |   2 +-
> fs/cifs/smb2ops.c                |  10 ++--
> fs/cifs/smb2pdu.c                |   6 +-
> fs/cifs/smb2proto.h              |  14 +++--
> fs/fcntl.c                       |   5 +-
> fs/locks.c                       | 121 ++++++++++++++++++++++++++++++++++++---
> fs/namei.c                       |  10 +++-
> fs/nfs/nfs4xdr.c                 |  24 ++++++--
> fs/nfsd/nfs4state.c              |  46 ++++++++++++++-
> include/linux/fs.h               |   6 ++
> include/uapi/asm-generic/fcntl.h |  14 +++++
> 23 files changed, 324 insertions(+), 96 deletions(-)
> 
> -- 
> 1.8.1.1
> 
> --
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