RE: [PATCH v7 0/7] Add O_DENY* support for VFS and CIFS/NFS

[Frank Filz]

This looks wonderful and will be useful to the Ganesha user space NFS server
also.

I do have a couple questions.

1. How will this interact with the idea of private locks from the patch set
Jeff Layton has been pushing?

2. If a process opens multiple file descriptors with deny modes, will they
conflict with each other (which is the behavior we will want for Ganesha).

3. Is there any functionality to upgrade or downgrade the access and deny
modes (thinking in terms of NFS v4 support of OPEN upgrade and
OPEN_DOWNGRADE operations).

Thanks

Frank

> -----Original Message-----
> From: linux-nfs-owner@xxxxxxxxxxxxxxx [mailto:linux-nfs-
> owner@xxxxxxxxxxxxxxx] On Behalf Of Pavel Shilovsky
> Sent: Friday, January 17, 2014 2:07 AM
> To: linux-kernel@xxxxxxxxxxxxxxx
> Cc: linux-cifs@xxxxxxxxxxxxxxx; linux-fsdevel@xxxxxxxxxxxxxxx; linux-
> nfs@xxxxxxxxxxxxxxx; wine-devel@xxxxxxxxxx
> Subject: [PATCH v7 0/7] Add O_DENY* support for VFS and CIFS/NFS
> 
> 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 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
> 
> The patchset avoids data races problem on newely created files: open with
> O_CREAT can return the -ESHAREDENIED error for a successfully created file
> if this files was locked with a sharelock by another task. Also, it turns
> flock/LOCK_MAND capability off for mounts with 'sharelock' option. This
lets
> not mix one share reservation approach with another.
> 
> Patches #1, #2 and #3 add O_DENY* flags to fcntl and implement VFS part. A
> patch #4 is related to CIFS client changes, #5 -- NFSD, #6 and #7 describe
> NFSv4 client 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 -ESHAREDENIED in following cases:
> 1) if O_DENYREAD flag is specified and there is another open with READ
> access to the file;
> 2) if O_DENYWRITE flag is specified and there is another open with WRITE
> access to the file;
> 3) if READ access is requested and there is another open with O_DENYREAD
> flags;
> 4) if WRITE access is requested and there is another open with
> O_DENYWRITE flags.
> 
> If O_DENYDELETE flag is specified and the open succeded, any further
unlink
> operation will fail with -ESHAREDENIED untill this open is closed. Now
this flag
> is processed by VFS and CIFS filesystem. NFS returns -EINVAL for opens
with
> this flag.
> 
> 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
> 3) !O_DENYDELETE -> LOCK_DELETE | LOCK_MAND
> -----
> 
> Pavel Shilovsky (7):
>   VFS: Introduce new O_DENY* open flags
>   VFS: Add O_DENYDELETE support for VFS
>   locks: Disable LOCK_MAND support for MS_SHARELOCK mounts
>   CIFS: Add O_DENY* open flags support
>   NFSD: Pass share reservations flags to VFS
>   NFSv4: Add deny state handling for nfs4_state struct
>   NFSv4: Add O_DENY* open flags support
> 
>  arch/alpha/include/uapi/asm/errno.h  |    2 +
>  arch/alpha/include/uapi/asm/fcntl.h  |    3 +
>  arch/mips/include/uapi/asm/errno.h   |    2 +
>  arch/parisc/include/uapi/asm/errno.h |    2 +
>  arch/parisc/include/uapi/asm/fcntl.h |    3 +
>  arch/sparc/include/uapi/asm/errno.h  |    2 +
>  arch/sparc/include/uapi/asm/fcntl.h  |    3 +
>  fs/cifs/cifsacl.c                    |    2 +
>  fs/cifs/cifsfs.c                     |    2 +-
>  fs/cifs/cifsglob.h                   |   17 +-
>  fs/cifs/cifssmb.c                    |    2 +-
>  fs/cifs/dir.c                        |    6 +
>  fs/cifs/file.c                       |   20 ++-
>  fs/cifs/inode.c                      |   12 +-
>  fs/cifs/link.c                       |    2 +
>  fs/cifs/netmisc.c                    |    2 +-
>  fs/cifs/smb1ops.c                    |    3 +
>  fs/cifs/smb2inode.c                  |    1 +
>  fs/cifs/smb2maperror.c               |    2 +-
>  fs/cifs/smb2ops.c                    |    6 +
>  fs/cifs/smb2pdu.c                    |    2 +-
>  fs/fcntl.c                           |    5 +-
>  fs/locks.c                           |  161 ++++++++++++++++--
>  fs/namei.c                           |   56 +++++-
>  fs/nfs/dir.c                         |   39 ++++-
>  fs/nfs/inode.c                       |    8 +-
>  fs/nfs/internal.h                    |    3 +-
>  fs/nfs/nfs4_fs.h                     |   83 ++++++++-
>  fs/nfs/nfs4file.c                    |    8 +-
>  fs/nfs/nfs4proc.c                    |  310
+++++++++++++++++++++++-----------
>  fs/nfs/nfs4state.c                   |   65 ++++---
>  fs/nfs/nfs4super.c                   |    9 +-
>  fs/nfs/nfs4xdr.c                     |   21 ++-
>  fs/nfs/super.c                       |    7 +-
>  fs/nfsd/nfs4state.c                  |   46 ++++-
>  fs/nfsd/nfsproc.c                    |    1 +
>  fs/proc_namespace.c                  |    1 +
>  include/linux/fs.h                   |   15 ++
>  include/linux/nfs_fs.h               |    5 +-
>  include/linux/nfs_xdr.h              |    1 +
>  include/uapi/asm-generic/errno.h     |    2 +
>  include/uapi/asm-generic/fcntl.h     |   12 ++
>  include/uapi/linux/fs.h              |    1 +
>  43 files changed, 789 insertions(+), 166 deletions(-)
> 
> --
> 1.7.10.4
> 
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