Re: [PATCH v7 0/7] Add O_DENY* support for VFS and CIFS/NFS
From: Pavel Shilovsky
Date: Fri Jan 31 2014 - 10:52:03 EST
2014-01-17 Pavel Shilovsky <piastry@xxxxxxxxxxx>:
> 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
>
Any other thoughts/reviews on this patchset?
--
Best regards,
Pavel Shilovsky.
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