Re: [PATCH v6 2/7] VFS: Add O_DENYDELETE support for VFS

From: Jeff Layton
Date: Fri May 10 2013 - 07:18:19 EST

On Fri, 26 Apr 2013 16:04:16 +0400
Pavel Shilovsky <piastry@xxxxxxxxxxx> wrote:

> Introduce new LOCK_DELETE flock flag that is suggested to be used
> internally only to map O_DENYDELETE open flag:
>
> !O_DENYDELETE -> LOCK_DELETE | LOCK_MAND.
>
> Signed-off-by: Pavel Shilovsky <piastry@xxxxxxxxxxx>
> ---
> fs/locks.c | 53 +++++++++++++++++++++++++++++++++-------
> fs/namei.c | 3 +++
> include/linux/fs.h | 6 +++++
> include/uapi/asm-generic/fcntl.h | 1 +
> 4 files changed, 54 insertions(+), 9 deletions(-)
>
> diff --git a/fs/locks.c b/fs/locks.c
> index dbc5557..1cc68a9 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -269,7 +269,7 @@ EXPORT_SYMBOL(locks_copy_lock);
>
> static inline int flock_translate_cmd(int cmd) {
> if (cmd & LOCK_MAND)
> - return cmd & (LOCK_MAND | LOCK_RW);
> + return cmd & (LOCK_MAND | LOCK_RW | LOCK_DELETE);
> switch (cmd) {
> case LOCK_SH:
> return F_RDLCK;
> @@ -614,6 +614,8 @@ deny_flags_to_cmd(unsigned int flags)
> cmd |= LOCK_READ;
> if (!(flags & O_DENYWRITE))
> cmd |= LOCK_WRITE;
> + if (!(flags & O_DENYDELETE))
> + cmd |= LOCK_DELETE;
>
> return cmd;
> }
> @@ -836,6 +838,31 @@ out:
> return error;
> }
>
> +int
> +sharelock_may_delete(struct dentry *dentry)
> +{
> + struct file_lock **before;
> + int rc = 0;
> +
> + if (!IS_SHARELOCK(dentry->d_inode))
> + return rc;
> +
> + lock_flocks();
> + for_each_lock(dentry->d_inode, before) {
> + struct file_lock *fl = *before;
> + if (IS_POSIX(fl))
> + break;
> + if (IS_LEASE(fl))
> + continue;
> + if (fl->fl_type & LOCK_DELETE)
> + continue;
> + rc = 1;
> + break;
> + }
> + unlock_flocks();
> + return rc;
> +}
> +
> /*
> * 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
> @@ -850,10 +877,6 @@ sharelock_lock_file(struct file *filp)
> 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;
> @@ -1717,6 +1740,12 @@ SYSCALL_DEFINE2(flock, unsigned int, fd, unsigned int, cmd)
> if (!f.file)
> goto out;
>
> + /* LOCK_DELETE is defined to be translated from O_DENYDELETE only */
> + if (cmd & LOCK_DELETE) {
> + error = -EINVAL;
> + goto out;
> + }
> +
> can_sleep = !(cmd & LOCK_NB);
> cmd &= ~LOCK_NB;
> unlock = (cmd == LOCK_UN);
> @@ -2261,10 +2290,16 @@ static void lock_get_status(struct seq_file *f, struct file_lock *fl,
> seq_printf(f, "UNKNOWN UNKNOWN ");
> }
> if (fl->fl_type & LOCK_MAND) {
> - seq_printf(f, "%s ",
> - (fl->fl_type & LOCK_READ)
> - ? (fl->fl_type & LOCK_WRITE) ? "RW " : "READ "
> - : (fl->fl_type & LOCK_WRITE) ? "WRITE" : "NONE ");
> + if (fl->fl_type & LOCK_DELETE)
> + seq_printf(f, "%s ",
> + (fl->fl_type & LOCK_READ) ?
> + (fl->fl_type & LOCK_WRITE) ? "RWDEL" : "RDDEL" :
> + (fl->fl_type & LOCK_WRITE) ? "WRDEL" : "DEL ");
> + else
> + seq_printf(f, "%s ",
> + (fl->fl_type & LOCK_READ) ?
> + (fl->fl_type & LOCK_WRITE) ? "RW " : "READ " :
> + (fl->fl_type & LOCK_WRITE) ? "WRITE" : "NONE ");
> } else {
> seq_printf(f, "%s ",
> (lease_breaking(fl))
> diff --git a/fs/namei.c b/fs/namei.c
> index dd236fe..a404f7d 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -2220,6 +2220,7 @@ static inline int check_sticky(struct inode *dir, struct inode *inode)
> * 9. We can't remove a root or mountpoint.
> * 10. We don't allow removal of NFS sillyrenamed files; it's handled by
> * nfs_async_unlink().
> + * 11. We can't do it if victim is locked by O_DENYDELETE sharelock.
> */
> static int may_delete(struct inode *dir,struct dentry *victim,int isdir)
> {
> @@ -2250,6 +2251,8 @@ static int may_delete(struct inode *dir,struct dentry *victim,int isdir)
> return -ENOENT;
> if (victim->d_flags & DCACHE_NFSFS_RENAMED)
> return -EBUSY;
> + if (sharelock_may_delete(victim))
> + return -ESHAREDENIED;


Is there a potential race here?

You're holding the parent's i_mutex when setting a lock on this file,
but you're not holding it when you test for it here. So it seems
possible you could end up granting a O_DENYDELETE open on a file that
is in the process of being deleted from the namespace.

> return 0;
> }
>
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 24066d2..afd56b1 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1006,6 +1006,7 @@ 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 void locks_delete_block(struct file_lock *waiter);
> extern int sharelock_lock_file(struct file *);
> +extern int sharelock_may_delete(struct dentry *);
> extern void lock_flocks(void);
> extern void unlock_flocks(void);
> #else /* !CONFIG_FILE_LOCKING */
> @@ -1159,6 +1160,11 @@ static inline int sharelock_lock_file(struct file *filp)
> return 0;
> }
>
> +static inline int sharelock_may_delete(struct dentry *dentry)
> +{
> + return 0;
> +}
> +
> static inline void lock_flocks(void)
> {
> }
> diff --git a/include/uapi/asm-generic/fcntl.h b/include/uapi/asm-generic/fcntl.h
> index 5ac0d49..a3e6349 100644
> --- a/include/uapi/asm-generic/fcntl.h
> +++ b/include/uapi/asm-generic/fcntl.h
> @@ -167,6 +167,7 @@ struct f_owner_ex {
> blocking */
> #define LOCK_UN 8 /* remove lock */
>
> +#define LOCK_DELETE 16 /* which allows to delete a file */
> #define LOCK_MAND 32 /* This is a mandatory flock ... */
> #define LOCK_READ 64 /* which allows concurrent read operations */
> #define LOCK_WRITE 128 /* which allows concurrent write operations */


--
Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
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