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

From: Jeff Layton
Date: Sat Feb 01 2014 - 08:21:20 EST

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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.

> 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.

> #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.

> + /*
> + * 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() ?).

> #ifndef O_NDELAY
> #define O_NDELAY O_NONBLOCK
> #endif
> diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> index 6c28b61..11f0ecf 100644
> --- a/include/uapi/linux/fs.h
> +++ b/include/uapi/linux/fs.h
> @@ -86,6 +86,7 @@ struct inodes_stat_t {
> #define MS_KERNMOUNT (1<<22) /* this is a kern_mount call */
> #define MS_I_VERSION (1<<23) /* Update inode I_version field */
> #define MS_STRICTATIME (1<<24) /* Always perform atime updates */
> +#define MS_SHARELOCK (1<<25) /* Allow share locks on an FS */
>
> /* These sb flags are internal to the kernel */
> #define MS_NOSEC (1<<28)

--
Jeff Layton <jlayton@xxxxxxxxxx>
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