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

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On Tue, 4 Feb 2014 16:03:14 +0400
Pavel Shilovsky <piastry@xxxxxxxxxxx> wrote:

> 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?
> 


Right, something that like that maybe...

...or possibly consider not making this specific to deny modes or
anything, and just consider adding a new generic "openat2()" syscall.

This one could have a larger (or maybe extensible) field for flags,
and well-defined behavior when presented with a flag that it doesn't
understand.

I realize that that's a large increase in scope, but it can often be
easier to get new features merged if you are simultaneously addressing
other problems that exist. ;)

-- 
Jeff Layton <jlayton@xxxxxxxxxx>
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