[PATCH v6 2/7] VFS: Add O_DENYDELETE support for VFS
Pavel Shilovsky
piastry at etersoft.ru
Mon May 13 12:50:23 CDT 2013
2013/5/10 Jeff Layton <jlayton at poochiereds.net>:
> On Fri, 26 Apr 2013 16:04:16 +0400
> Pavel Shilovsky <piastry at etersoft.ru> 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 at etersoft.ru>
>> ---
>> 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.
may_delete function is called from vfs_unlnk, vfs_rename and vfs_rmdir
and in all those places the caller is holding parent's i_mutex. It
seems that the locking order is correct: we hold parent's i_mutex when
we set and test sharelocks.
>> 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 at poochiereds.net>
> --
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--
Best regards,
Pavel Shilovsky.
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