by Jeff Layton

[permalink] [raw]

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

On Tue, 4 Feb 2014 16:03:14 +0400
Pavel Shilovsky <[email protected]> wrote:

> 2014-02-01 Jeff Layton <[email protected]>:
> > On Fri, 17 Jan 2014 14:07:06 +0400
> > Pavel Shilovsky <[email protected]> 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 <[email protected]>
> >> ---
> >> 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 <[email protected]>