[PATCH v2 0/8] Add O_DENY* support for VFS and CIFS/NFS
J. Bruce Fields
bfields at fieldses.org
Wed Jan 30 16:11:18 CST 2013
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?
> 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:
> 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(-)
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