[PATCH v4 0/7] Add O_DENY* support for VFS and CIFS/NFS

[Pavel Shilovsky]

Main changes from the previous one:
1) O_DENYMAND is removed, sharelock mount option is introduced.
2) Patch fcntl.h and VFS patches are united into one.
3) flock/LOCK_MAND is disabled for sharelock mounts.

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 extra mount option 'sharelock' is added for switching on/off O_DENY* flags processing. It allows us to avoid use of these flags on critical places (like /, /lib) and turn them on if we really want it proccessed that way.

So, we have 3 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),

The patchset avoid data races problem on newely created files: open with O_CREAT can return the -ETXTBSY error for a successfully created file if this files was locked with a deny lock by another task. Also, it turns flock/LOCK_MAND capability off for mounts with 'sharelock' option. This let us not mix one share reservation approach with another.

The #1 patch adds flags to fcntl and implements VFS part. The patches #3, #4, #5 are related to CIFS-specific changes, #6 and #7 describe NFS and NFSD parts.

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=173070262b7f29134ad6b2e49a760017c11aec4a

The future part of open man page patch:

-----
O_DENYREAD, O_DENYWRIYE, O_DENYDELETE - used to inforce a mandatory share reservation scheme of the file access. If these flag is passed, the open fails with -EBUSY in following cases:
1) if O_DENYREAD flag is specified and there is another open with O_DENYMAND flag and READ access to the file;
2) if O_DENYWRITE flag is specified and there is another open with O_DENYMAND flag and WRITE access to the file;
3) if READ access is requested and there is another open with O_DENYMAND and O_DENYREAD flags;
4) if WRITE access is requested and there is another open with O_DENYMAND and O_DENYWRITE flags.

If O_DENYDELETE flag is specified and the open succeded, any further unlink operation will fail with -EBUSY untill this open is closed. Now this flag is processed by CIFS filesystems only.

This mechanism is done through flocks. If O_DENY* flags are specified, flock syscall is processed after the open. The share modes are translated into flock according the following rules:
1) !O_DENYREAD  -> LOCK_READ | LOCK_MAND
2) !O_DENYWRITE -> LOCK_WRITE | LOCK_MAND
-----

Pavel Shilovsky (7):
  fcntl: Introduce new O_DENY* open flags
  CIFS: Add share_access parm to open request
  CIFS: Add O_DENY* open flags support
  CIFS: Use NT_CREATE_ANDX command for forcemand mounts
  NFSv4: Add O_DENY* open flags support
  NFSD: Pass share reservations flags to VFS
  locks: Disable LOCK_MAND support for MS_SHARELOCK mounts

 fs/cifs/cifsacl.c                |   8 +--
 fs/cifs/cifsglob.h               |  18 ++++++-
 fs/cifs/cifsproto.h              |   8 +--
 fs/cifs/cifssmb.c                |  50 +++++++++---------
 fs/cifs/dir.c                    |  16 +++---
 fs/cifs/file.c                   |  20 +++++---
 fs/cifs/inode.c                  |  16 +++---
 fs/cifs/link.c                   |  25 +++------
 fs/cifs/readdir.c                |   5 +-
 fs/cifs/smb1ops.c                |  16 +++---
 fs/cifs/smb2file.c               |  10 ++--
 fs/cifs/smb2inode.c              |   4 +-
 fs/cifs/smb2ops.c                |  10 ++--
 fs/cifs/smb2pdu.c                |   6 +--
 fs/cifs/smb2proto.h              |  14 ++---
 fs/fcntl.c                       |   5 +-
 fs/locks.c                       | 108 ++++++++++++++++++++++++++++++++++++---
 fs/namei.c                       |  45 ++++++++++++++--
 fs/nfs/internal.h                |   3 +-
 fs/nfs/nfs4proc.c                |   2 +
 fs/nfs/nfs4xdr.c                 |  21 ++++++--
 fs/nfs/super.c                   |   3 +-
 fs/nfsd/nfs4state.c              |  46 ++++++++++++++++-
 fs/proc_namespace.c              |   1 +
 include/linux/fs.h               |   7 +++
 include/uapi/asm-generic/fcntl.h |  11 ++++
 include/uapi/linux/fs.h          |   1 +
 27 files changed, 355 insertions(+), 124 deletions(-)

-- 
1.8.1.5

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/