Re: [PATCH v7 1/7] VFS: Introduce new O_DENY* open flags

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2014-02-01 Jeff Layton <jlayton@xxxxxxxxxx>:
> On Fri, 17 Jan 2014 14:07:06 +0400
> Pavel Shilovsky <piastry@xxxxxxxxxxx> wrote:
>
>> This patch adds 3 flags:
>> 1) O_DENYREAD that doesn't permit read access,
>> 2) O_DENYWRITE that doesn't permit write access,
>> 3) O_DENYDELETE that doesn't permit delete or rename.
>>
>> Network filesystems CIFS, SMB2.0, SMB3.0 and NFSv4 have such flags -
>> this change can benefit cifs and nfs modules as well as Samba and
>> NFS file servers that export the same directory for Windows clients,
>> or Wine applications that access the same files simultaneously.
>>
>> These flags are only take affect for opens on mounts with new sharelock
>> option. They are translated to flock's flags:
>>
>> !O_DENYREAD  -> LOCK_READ  | LOCK_MAND
>> !O_DENYWRITE -> LOCK_WRITE | LOCK_MAND
>>
>> and set through flock_lock_file on a file. If the file can't be locked
>> due conflicts with another open with O_DENY* flags, a new -ESHAREDENIED
>> error code is returned.
>>
>> Create codepath is slightly changed to prevent data races on newly
>> created files: when open with O_CREAT can return -ESHAREDENIED error
>> for successfully created files due to a sharelock set by another task.
>>
>> Temporary disable O_DENYDELETE support - will enable it in further
>> patches.
>>
>> Signed-off-by: Pavel Shilovsky <piastry@xxxxxxxxxxx>
>> ---
>>  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/fcntl.c                           |    5 +-
>>  fs/locks.c                           |   97 +++++++++++++++++++++++++++++++---
>>  fs/namei.c                           |   53 ++++++++++++++++++-
>>  fs/proc_namespace.c                  |    1 +
>>  include/linux/fs.h                   |    8 +++
>>  include/uapi/asm-generic/errno.h     |    2 +
>>  include/uapi/asm-generic/fcntl.h     |   11 ++++
>>  include/uapi/linux/fs.h              |    1 +
>>  15 files changed, 185 insertions(+), 10 deletions(-)
>>
>
> You might consider breaking this patch into two. One patch that makes
> LOCK_MAND locks actually work and that adds MS_SHARELOCK, and one patch
> that hooks that up to open(). Given the locking involved with the
> i_mutex it would be best to present this as a series of small,
> incremental changes.

Good point. So, we can break it into 2:
1) make flock actually work with LOCK_MAND on MS_SHARELOCK mounts,
2) replace flock+LOCK_MAND with open+O_DENY* flags.


>> diff --git a/arch/alpha/include/uapi/asm/errno.h b/arch/alpha/include/uapi/asm/errno.h
>> index 17f92aa..953a6d6 100644
>> --- a/arch/alpha/include/uapi/asm/errno.h
>> +++ b/arch/alpha/include/uapi/asm/errno.h
>> @@ -124,4 +124,6 @@
>>
>>  #define EHWPOISON    139     /* Memory page has hardware error */
>>
>> +#define ESHAREDENIED 140     /* File is locked with a sharelock */
>> +
>>  #endif
>> diff --git a/arch/alpha/include/uapi/asm/fcntl.h b/arch/alpha/include/uapi/asm/fcntl.h
>> index 09f49a6..265344b 100644
>> --- a/arch/alpha/include/uapi/asm/fcntl.h
>> +++ b/arch/alpha/include/uapi/asm/fcntl.h
>> @@ -33,6 +33,9 @@
>>
>>  #define O_PATH               040000000
>>  #define __O_TMPFILE  0100000000
>> +#define O_DENYREAD   0200000000      /* Do not permit read access */
>> +#define O_DENYWRITE  0400000000      /* Do not permit write access */
>> +#define O_DENYDELETE 01000000000     /* Do not permit delete or rename */
>>
>>  #define F_GETLK              7
>>  #define F_SETLK              8
>> diff --git a/arch/mips/include/uapi/asm/errno.h b/arch/mips/include/uapi/asm/errno.h
>> index 02d645d..f1a4068 100644
>> --- a/arch/mips/include/uapi/asm/errno.h
>> +++ b/arch/mips/include/uapi/asm/errno.h
>> @@ -123,6 +123,8 @@
>>
>>  #define EHWPOISON    168     /* Memory page has hardware error */
>>
>> +#define ESHAREDENIED 169     /* File is locked with a sharelock */
>> +
>>  #define EDQUOT               1133    /* Quota exceeded */
>>
>>
>> diff --git a/arch/parisc/include/uapi/asm/errno.h b/arch/parisc/include/uapi/asm/errno.h
>> index f3a8aa5..654c232 100644
>> --- a/arch/parisc/include/uapi/asm/errno.h
>> +++ b/arch/parisc/include/uapi/asm/errno.h
>> @@ -124,4 +124,6 @@
>>
>>  #define EHWPOISON    257     /* Memory page has hardware error */
>>
>> +#define ESHAREDENIED 258     /* File is locked with a sharelock */
>> +
>>  #endif
>> diff --git a/arch/parisc/include/uapi/asm/fcntl.h b/arch/parisc/include/uapi/asm/fcntl.h
>> index 34a46cb..5865964 100644
>> --- a/arch/parisc/include/uapi/asm/fcntl.h
>> +++ b/arch/parisc/include/uapi/asm/fcntl.h
>> @@ -21,6 +21,9 @@
>>
>>  #define O_PATH               020000000
>>  #define __O_TMPFILE  040000000
>> +#define O_DENYREAD   0200000000      /* Do not permit read access */
>> +#define O_DENYWRITE  0400000000      /* Do not permit write access */
>> +#define O_DENYDELETE 01000000000     /* Do not permit delete or rename */
>>
>>  #define F_GETLK64    8
>>  #define F_SETLK64    9
>> diff --git a/arch/sparc/include/uapi/asm/errno.h b/arch/sparc/include/uapi/asm/errno.h
>> index 20423e17..fe339b5 100644
>> --- a/arch/sparc/include/uapi/asm/errno.h
>> +++ b/arch/sparc/include/uapi/asm/errno.h
>> @@ -114,4 +114,6 @@
>>
>>  #define EHWPOISON    135     /* Memory page has hardware error */
>>
>> +#define ESHAREDENIED 136     /* File is locked with a sharelock */
>> +
>>  #endif
>> diff --git a/arch/sparc/include/uapi/asm/fcntl.h b/arch/sparc/include/uapi/asm/fcntl.h
>> index 7e8ace5..ab68170 100644
>> --- a/arch/sparc/include/uapi/asm/fcntl.h
>> +++ b/arch/sparc/include/uapi/asm/fcntl.h
>> @@ -36,6 +36,9 @@
>>
>>  #define O_PATH               0x1000000
>>  #define __O_TMPFILE  0x2000000
>> +#define O_DENYREAD   0x4000000       /* Do not permit read access */
>> +#define O_DENYWRITE  0x8000000       /* Do not permit write access */
>> +#define O_DENYDELETE 0x10000000      /* Do not permit delete or rename */
>>
>
> It'd probably be best to add O_DENYDELETE in a separate patch, rather
> than disabling it temporarily.

Agree.

>
>>  #define F_GETOWN     5       /*  for sockets. */
>>  #define F_SETOWN     6       /*  for sockets. */
>> diff --git a/fs/fcntl.c b/fs/fcntl.c
>> index ef68665..3f85887 100644
>> --- a/fs/fcntl.c
>> +++ b/fs/fcntl.c
>> @@ -729,14 +729,15 @@ static int __init fcntl_init(void)
>>        * Exceptions: O_NONBLOCK is a two bit define on parisc; O_NDELAY
>>        * is defined as O_NONBLOCK on some platforms and not on others.
>>        */
>> -     BUILD_BUG_ON(20 - 1 /* for O_RDONLY being 0 */ != HWEIGHT32(
>> +     BUILD_BUG_ON(23 - 1 /* for O_RDONLY being 0 */ != HWEIGHT32(
>>               O_RDONLY        | O_WRONLY      | O_RDWR        |
>>               O_CREAT         | O_EXCL        | O_NOCTTY      |
>>               O_TRUNC         | O_APPEND      | /* O_NONBLOCK | */
>>               __O_SYNC        | O_DSYNC       | FASYNC        |
>>               O_DIRECT        | O_LARGEFILE   | O_DIRECTORY   |
>>               O_NOFOLLOW      | O_NOATIME     | O_CLOEXEC     |
>> -             __FMODE_EXEC    | O_PATH        | __O_TMPFILE
>> +             __FMODE_EXEC    | O_PATH        | __O_TMPFILE   |
>> +             O_DENYREAD      | O_DENYWRITE   | O_DENYDELETE
>>               ));
>>
>>       fasync_cache = kmem_cache_create("fasync_cache",
>> diff --git a/fs/locks.c b/fs/locks.c
>> index 92a0f0a..ffde4d4 100644
>> --- a/fs/locks.c
>> +++ b/fs/locks.c
>> @@ -708,20 +708,73 @@ static int posix_locks_conflict(struct file_lock *caller_fl, struct file_lock *s
>>       return (locks_conflict(caller_fl, sys_fl));
>>  }
>>
>> -/* Determine if lock sys_fl blocks lock caller_fl. FLOCK specific
>> - * checking before calling the locks_conflict().
>> +static unsigned int
>> +deny_flags_to_cmd(unsigned int flags)
>> +{
>> +     unsigned int cmd = LOCK_MAND;
>> +
>> +     if (!(flags & O_DENYREAD))
>> +             cmd |= LOCK_READ;
>> +     if (!(flags & O_DENYWRITE))
>> +             cmd |= LOCK_WRITE;
>> +
>> +     return cmd;
>> +}
>> +
>> +/*
>> + * locks_mand_conflict - Determine if there's a share reservation conflict
>> + * @caller_fl: lock we're attempting to acquire
>> + * @sys_fl: lock already present on system that we're checking against
>> + *
>> + * Check to see if there's a share_reservation conflict. LOCK_READ/LOCK_WRITE
>> + * tell us whether the reservation allows other readers and writers.
>> + */
>> +static int
>> +locks_mand_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
>> +{
>> +     unsigned char caller_type = caller_fl->fl_type;
>> +     unsigned char sys_type = sys_fl->fl_type;
>> +     fmode_t caller_fmode = caller_fl->fl_file->f_mode;
>> +     fmode_t sys_fmode = sys_fl->fl_file->f_mode;
>> +
>> +     /* they can only conflict if FS is mounted with MS_SHARELOCK */
>> +     if (!IS_SHARELOCK(caller_fl->fl_file->f_path.dentry->d_inode))
>> +             return 0;
>> +
>> +     /* they can only conflict if they're both LOCK_MAND */
>> +     if (!(caller_type & LOCK_MAND) || !(sys_type & LOCK_MAND))
>> +             return 0;
>> +
>> +     if (!(caller_type & LOCK_READ) && (sys_fmode & FMODE_READ))
>> +             return 1;
>> +     if (!(caller_type & LOCK_WRITE) && (sys_fmode & FMODE_WRITE))
>> +             return 1;
>> +     if (!(sys_type & LOCK_READ) && (caller_fmode & FMODE_READ))
>> +             return 1;
>> +     if (!(sys_type & LOCK_WRITE) && (caller_fmode & FMODE_WRITE))
>> +             return 1;
>> +
>> +     return 0;
>> +}
>> +
>> +/*
>> + * Determine if lock sys_fl blocks lock caller_fl. FLOCK specific checking
>> + * before calling the locks_conflict().
>>   */
>>  static int flock_locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
>>  {
>> -     /* FLOCK locks referring to the same filp do not conflict with
>> +     if (!IS_FLOCK(sys_fl))
>> +             return 0;
>> +     if ((caller_fl->fl_type & LOCK_MAND) || (sys_fl->fl_type & LOCK_MAND))
>> +             return locks_mand_conflict(caller_fl, sys_fl);
>
> nit: Seems like the above could be optimized a little. You know that
> locks_mand_conflict is only relevant if both are LOCK_MAND, and one of
> the first things that locks_mand_conflict does is to check that both
> have that set.

ok.

>
>> +     /*
>> +      * FLOCK locks referring to the same filp do not conflict with
>>        * each other.
>>        */
>> -     if (!IS_FLOCK(sys_fl) || (caller_fl->fl_file == sys_fl->fl_file))
>> -             return (0);
>> -     if ((caller_fl->fl_type & LOCK_MAND) || (sys_fl->fl_type & LOCK_MAND))
>> +     if (caller_fl->fl_file == sys_fl->fl_file)
>>               return 0;
>>
>> -     return (locks_conflict(caller_fl, sys_fl));
>> +     return locks_conflict(caller_fl, sys_fl);
>>  }
>>
>>  void
>> @@ -888,6 +941,36 @@ out:
>>       return error;
>>  }
>>
>> +/*
>> + * Determine if a file is allowed to be opened with specified access and share
>> + * modes. Lock the file and return 0 if checks passed, otherwise return
>> + * -ESHAREDENIED.
>> + */
>> +int
>> +sharelock_lock_file(struct file *filp)
>> +{
>> +     struct file_lock *lock;
>> +     int error = 0;
>> +
>> +     if (!IS_SHARELOCK(filp->f_path.dentry->d_inode))
>> +             return error;
>> +
>> +     /* Disable O_DENYDELETE support for now */
>> +     if (filp->f_flags & O_DENYDELETE)
>> +             return -EINVAL;
>> +
>> +     error = flock_make_lock(filp, &lock, deny_flags_to_cmd(filp->f_flags));
>> +     if (error)
>> +             return error;
>> +
>> +     error = flock_lock_file(filp, lock);
>> +     if (error == -EAGAIN)
>> +             error = -ESHAREDENIED;
>> +
>> +     locks_free_lock(lock);
>> +     return error;
>> +}
>> +
>>  static int __posix_lock_file(struct inode *inode, struct file_lock *request, struct file_lock *conflock)
>>  {
>>       struct file_lock *fl;
>> diff --git a/fs/namei.c b/fs/namei.c
>> index 3531dee..2b741a1 100644
>> --- a/fs/namei.c
>> +++ b/fs/namei.c
>> @@ -2725,9 +2725,14 @@ static int atomic_open(struct nameidata *nd, struct dentry *dentry,
>>               acc_mode = MAY_OPEN;
>>       }
>>       error = may_open(&file->f_path, acc_mode, open_flag);
>> -     if (error)
>> +     if (error) {
>>               fput(file);
>> +             goto out;
>> +     }
>>
>> +     error = sharelock_lock_file(file);
>> +     if (error)
>> +             fput(file);
>>  out:
>>       dput(dentry);
>>       return error;
>> @@ -2919,6 +2924,40 @@ retry_lookup:
>>       }
>>       mutex_lock(&dir->d_inode->i_mutex);
>>       error = lookup_open(nd, path, file, op, got_write, opened);
>> +
>> +     /*
>> +      * For sharelock mounts if a file was created but not opened, we need
>> +      * to keep parent i_mutex until we finish the open to prevent races when
>> +      * somebody opens newly created by us file and locks it with a sharelock
>> +      * before we open it.
>> +      */
>> +     if (IS_SHARELOCK(dir->d_inode) && error > 0 && *opened & FILE_CREATED) {
>> +             /* Don't check for write permission, don't truncate */
>> +             open_flag &= ~O_TRUNC;
>> +             will_truncate = false;
>> +             acc_mode = MAY_OPEN;
>> +             path_to_nameidata(path, nd);
>> +
>> +             error = may_open(&nd->path, acc_mode, open_flag);
>> +             if (error) {
>> +                     mutex_unlock(&dir->d_inode->i_mutex);
>> +                     goto out;
>> +             }
>> +             file->f_path.mnt = nd->path.mnt;
>> +             error = finish_open(file, nd->path.dentry, NULL, opened);
>> +             if (error) {
>> +                     mutex_unlock(&dir->d_inode->i_mutex);
>> +                     if (error == -EOPENSTALE)
>> +                             goto stale_open;
>> +                     goto out;
>> +             }
>> +             error = sharelock_lock_file(file);
>> +             mutex_unlock(&dir->d_inode->i_mutex);
>> +             if (error)
>> +                     goto exit_fput;
>> +             goto opened;
>> +     }
>> +
>>       mutex_unlock(&dir->d_inode->i_mutex);
>>
>>       if (error <= 0) {
>> @@ -3034,6 +3073,18 @@ finish_open_created:
>>                       goto stale_open;
>>               goto out;
>>       }
>> +
>> +     if (IS_SHARELOCK(dir->d_inode)) {
>> +             /*
>> +              * Lock parent i_mutex to prevent races with sharelocks on
>> +              * newly created files.
>> +              */
>> +             mutex_lock(&dir->d_inode->i_mutex);
>> +             error = sharelock_lock_file(file);
>> +             mutex_unlock(&dir->d_inode->i_mutex);
>> +             if (error)
>> +                     goto exit_fput;
>> +     }
>>  opened:
>>       error = open_check_o_direct(file);
>>       if (error)
>> diff --git a/fs/proc_namespace.c b/fs/proc_namespace.c
>> index 439406e..dd374d4 100644
>> --- a/fs/proc_namespace.c
>> +++ b/fs/proc_namespace.c
>> @@ -44,6 +44,7 @@ static int show_sb_opts(struct seq_file *m, struct super_block *sb)
>>               { MS_SYNCHRONOUS, ",sync" },
>>               { MS_DIRSYNC, ",dirsync" },
>>               { MS_MANDLOCK, ",mand" },
>> +             { MS_SHARELOCK, ",sharelock" },
>>               { 0, NULL }
>>       };
>>       const struct proc_fs_info *fs_infop;
>> diff --git a/include/linux/fs.h b/include/linux/fs.h
>> index 121f11f..aa061ca 100644
>> --- a/include/linux/fs.h
>> +++ b/include/linux/fs.h
>> @@ -1029,6 +1029,7 @@ extern int vfs_setlease(struct file *, long, struct file_lock **);
>>  extern int lease_modify(struct file_lock **, int);
>>  extern int lock_may_read(struct inode *, loff_t start, unsigned long count);
>>  extern int lock_may_write(struct inode *, loff_t start, unsigned long count);
>> +extern int sharelock_lock_file(struct file *);
>>  #else /* !CONFIG_FILE_LOCKING */
>>  static inline int fcntl_getlk(struct file *file, struct flock __user *user)
>>  {
>> @@ -1169,6 +1170,12 @@ static inline int lock_may_write(struct inode *inode, loff_t start,
>>  {
>>       return 1;
>>  }
>> +
>> +static inline int sharelock_lock_file(struct file *filp)
>> +{
>> +     return 0;
>> +}
>> +
>>  #endif /* !CONFIG_FILE_LOCKING */
>>
>>
>> @@ -1675,6 +1682,7 @@ struct super_operations {
>>  #define IS_PRIVATE(inode)    ((inode)->i_flags & S_PRIVATE)
>>  #define IS_IMA(inode)                ((inode)->i_flags & S_IMA)
>>  #define IS_AUTOMOUNT(inode)  ((inode)->i_flags & S_AUTOMOUNT)
>> +#define IS_SHARELOCK(inode)  __IS_FLG(inode, MS_SHARELOCK)
>>  #define IS_NOSEC(inode)              ((inode)->i_flags & S_NOSEC)
>>
>>  /*
>> diff --git a/include/uapi/asm-generic/errno.h b/include/uapi/asm-generic/errno.h
>> index 1e1ea6e..aff869c 100644
>> --- a/include/uapi/asm-generic/errno.h
>> +++ b/include/uapi/asm-generic/errno.h
>> @@ -110,4 +110,6 @@
>>
>>  #define EHWPOISON    133     /* Memory page has hardware error */
>>
>> +#define ESHAREDENIED 134     /* File is locked with a sharelock */
>> +
>>  #endif
>> diff --git a/include/uapi/asm-generic/fcntl.h b/include/uapi/asm-generic/fcntl.h
>> index 95e46c8..9881cfe 100644
>> --- a/include/uapi/asm-generic/fcntl.h
>> +++ b/include/uapi/asm-generic/fcntl.h
>> @@ -92,6 +92,17 @@
>>  #define O_TMPFILE (__O_TMPFILE | O_DIRECTORY)
>>  #define O_TMPFILE_MASK (__O_TMPFILE | O_DIRECTORY | O_CREAT)
>>
>> +#ifndef O_DENYREAD
>> +#define O_DENYREAD   040000000       /* Do not permit read access */
>> +#endif
>> +/* FMODE_NONOTIFY    0100000000 */
>> +#ifndef O_DENYWRITE
>> +#define O_DENYWRITE  0200000000      /* Do not permit write access */
>> +#endif
>> +#ifndef O_DENYDELETE
>> +#define O_DENYDELETE 0400000000      /* Do not permit delete or rename */
>> +#endif
>> +
>
> One thing to consider: We found with the addition of O_TMPFILE that the
> open() api is not particularly helpful when it comes to informing
> appications when a flag isn't supported:
>
>     http://lwn.net/Articles/562294/
>
> ...having a plan to cope with that here would be best. How can an
> application determine at runtime that O_DENY* actually *work*? It may
> be best to step back and consider a new syscall for this (open2() ?).
>

So, consider we added new syscall:

opendm(filename, flags, mode, deny_mode)
{
  return open(filename, flags | denymode2openflags(deny_mode), mode)
}

where deny_mode can be DMODE_NONE (0), DMODE_READ (1), DMODE_WRITE(2)
and DMODE_RDWR(3) (similar to FMODE_* values).

We have open and opendm that act actually in the same manner for
mounts without MS_SHARELOCK. For mounts with MS_SHARELOCK open is like
opendm with DMODE_NONE. Open flags O_DENY* are for internal use only.

Is it what you suggest?

-- 
Best regards,
Pavel Shilovsky.
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