quota: Fix deadlock during path resolution

As Al Viro pointed out path resolution during Q_QUOTAON calls to quotactl
is prone to deadlocks. We hold s_umount semaphore for reading during the
path resolution and resolution itself may need to acquire the semaphore
for writing when e. g. autofs mountpoint is passed.

Solve the problem by performing the resolution before we get hold of the
superblock (and thus s_umount semaphore). The whole thing is complicated
by the fact that some filesystems (OCFS2) ignore the path argument. So to
distinguish between filesystem which want the path and which do not we
introduce new .quota_on_meta callback which does not get the path. OCFS2
then uses this callback instead of old .quota_on.

CC: Al Viro <viro@ZenIV.linux.org.uk>
CC: Christoph Hellwig <hch@lst.de>
CC: Ted Ts'o <tytso@mit.edu>
CC: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/ext3/super.c

@@ -755,7 +755,7 @@ static int ext3_release_dquot(struct dquot *dquot);
 static int ext3_mark_dquot_dirty(struct dquot *dquot);
 static int ext3_write_info(struct super_block *sb, int type);
 static int ext3_quota_on(struct super_block *sb, int type, int format_id,
-				char *path);
+			 struct path *path);
 static int ext3_quota_on_mount(struct super_block *sb, int type);
 static ssize_t ext3_quota_read(struct super_block *sb, int type, char *data,
 			       size_t len, loff_t off);
@@ -2885,27 +2885,20 @@ static int ext3_quota_on_mount(struct super_block *sb, int type)
  * Standard function to be called on quota_on
  */
 static int ext3_quota_on(struct super_block *sb, int type, int format_id,
-			 char *name)
+			 struct path *path)
 {
 	int err;
-	struct path path;
 
 	if (!test_opt(sb, QUOTA))
 		return -EINVAL;
 
-	err = kern_path(name, LOOKUP_FOLLOW, &path);
-	if (err)
-		return err;
-
 	/* Quotafile not on the same filesystem? */
-	if (path.mnt->mnt_sb != sb) {
+	if (path->mnt->mnt_sb != sb)
-		path_put(&path);
 		return -EXDEV;
-	}
 	/* Journaling quota? */
 	if (EXT3_SB(sb)->s_qf_names[type]) {
 		/* Quotafile not of fs root? */
-		if (path.dentry->d_parent != sb->s_root)
+		if (path->dentry->d_parent != sb->s_root)
 			ext3_msg(sb, KERN_WARNING,
 				"warning: Quota file not on filesystem root. "
 				"Journaled quota will not work.");
@@ -2915,7 +2908,7 @@ static int ext3_quota_on(struct super_block *sb, int type, int format_id,
 	 * When we journal data on quota file, we have to flush journal to see
 	 * all updates to the file when we bypass pagecache...
 	 */
-	if (ext3_should_journal_data(path.dentry->d_inode)) {
+	if (ext3_should_journal_data(path->dentry->d_inode)) {
 		/*
 		 * We don't need to lock updates but journal_flush() could
 		 * otherwise be livelocked...
@@ -2923,15 +2916,11 @@ static int ext3_quota_on(struct super_block *sb, int type, int format_id,
 		journal_lock_updates(EXT3_SB(sb)->s_journal);
 		err = journal_flush(EXT3_SB(sb)->s_journal);
 		journal_unlock_updates(EXT3_SB(sb)->s_journal);
-		if (err) {
+		if (err)
-			path_put(&path);
 			return err;
-		}
 	}
 
-	err = dquot_quota_on_path(sb, type, format_id, &path);
+	return dquot_quota_on(sb, type, format_id, path);
-	path_put(&path);
-	return err;
 }
 
 /* Read data from quotafile - avoid pagecache and such because we cannot afford

fs/ext4/super.c

@@ -1162,7 +1162,7 @@ static int ext4_release_dquot(struct dquot *dquot);
 static int ext4_mark_dquot_dirty(struct dquot *dquot);
 static int ext4_write_info(struct super_block *sb, int type);
 static int ext4_quota_on(struct super_block *sb, int type, int format_id,
-				char *path);
+			 struct path *path);
 static int ext4_quota_off(struct super_block *sb, int type);
 static int ext4_quota_on_mount(struct super_block *sb, int type);
 static ssize_t ext4_quota_read(struct super_block *sb, int type, char *data,
@@ -4566,27 +4566,20 @@ static int ext4_quota_on_mount(struct super_block *sb, int type)
  * Standard function to be called on quota_on
  */
 static int ext4_quota_on(struct super_block *sb, int type, int format_id,
-			 char *name)
+			 struct path *path)
 {
 	int err;
-	struct path path;
 
 	if (!test_opt(sb, QUOTA))
 		return -EINVAL;
 
-	err = kern_path(name, LOOKUP_FOLLOW, &path);
-	if (err)
-		return err;
-
 	/* Quotafile not on the same filesystem? */
-	if (path.mnt->mnt_sb != sb) {
+	if (path->mnt->mnt_sb != sb)
-		path_put(&path);
 		return -EXDEV;
-	}
 	/* Journaling quota? */
 	if (EXT4_SB(sb)->s_qf_names[type]) {
 		/* Quotafile not in fs root? */
-		if (path.dentry->d_parent != sb->s_root)
+		if (path->dentry->d_parent != sb->s_root)
 			ext4_msg(sb, KERN_WARNING,
 				"Quota file not on filesystem root. "
 				"Journaled quota will not work");
@@ -4597,7 +4590,7 @@ static int ext4_quota_on(struct super_block *sb, int type, int format_id,
 	 * all updates to the file when we bypass pagecache...
 	 */
 	if (EXT4_SB(sb)->s_journal &&
-	    ext4_should_journal_data(path.dentry->d_inode)) {
+	    ext4_should_journal_data(path->dentry->d_inode)) {
 		/*
 		 * We don't need to lock updates but journal_flush() could
 		 * otherwise be livelocked...
@@ -4605,15 +4598,11 @@ static int ext4_quota_on(struct super_block *sb, int type, int format_id,
 		jbd2_journal_lock_updates(EXT4_SB(sb)->s_journal);
 		err = jbd2_journal_flush(EXT4_SB(sb)->s_journal);
 		jbd2_journal_unlock_updates(EXT4_SB(sb)->s_journal);
-		if (err) {
+		if (err)
-			path_put(&path);
 			return err;
-		}
 	}
 
-	err = dquot_quota_on_path(sb, type, format_id, &path);
+	return dquot_quota_on(sb, type, format_id, path);
-	path_put(&path);
-	return err;
 }
 
 static int ext4_quota_off(struct super_block *sb, int type)

fs/ocfs2/super.c

@@ -993,8 +993,7 @@ static void ocfs2_disable_quotas(struct ocfs2_super *osb)
 }
 
 /* Handle quota on quotactl */
-static int ocfs2_quota_on(struct super_block *sb, int type, int format_id,
+static int ocfs2_quota_on(struct super_block *sb, int type, int format_id)
-			  char *path)
 {
 	unsigned int feature[MAXQUOTAS] = { OCFS2_FEATURE_RO_COMPAT_USRQUOTA,
 					     OCFS2_FEATURE_RO_COMPAT_GRPQUOTA};
@@ -1013,7 +1012,7 @@ static int ocfs2_quota_off(struct super_block *sb, int type)
 }
 
 static const struct quotactl_ops ocfs2_quotactl_ops = {
-	.quota_on	= ocfs2_quota_on,
+	.quota_on_meta	= ocfs2_quota_on,
 	.quota_off	= ocfs2_quota_off,
 	.quota_sync	= dquot_quota_sync,
 	.get_info	= dquot_get_dqinfo,

fs/quota/dquot.c

@@ -2189,8 +2189,8 @@ int dquot_resume(struct super_block *sb, int type)
 }
 EXPORT_SYMBOL(dquot_resume);
 
-int dquot_quota_on_path(struct super_block *sb, int type, int format_id,
+int dquot_quota_on(struct super_block *sb, int type, int format_id,
-		      struct path *path)
+		   struct path *path)
 {
 	int error = security_quota_on(path->dentry);
 	if (error)
@@ -2204,20 +2204,6 @@ int dquot_quota_on_path(struct super_block *sb, int type, int format_id,
 					     DQUOT_LIMITS_ENABLED);
 	return error;
 }
-EXPORT_SYMBOL(dquot_quota_on_path);
-
-int dquot_quota_on(struct super_block *sb, int type, int format_id, char *name)
-{
-	struct path path;
-	int error;
-
-	error = kern_path(name, LOOKUP_FOLLOW, &path);
-	if (!error) {
-		error = dquot_quota_on_path(sb, type, format_id, &path);
-		path_put(&path);
-	}
-	return error;
-}
 EXPORT_SYMBOL(dquot_quota_on);
 
 /*

fs/quota/quota.c

@@ -64,18 +64,15 @@ static int quota_sync_all(int type)
 }
 
 static int quota_quotaon(struct super_block *sb, int type, int cmd, qid_t id,
-		         void __user *addr)
+		         struct path *path)
 {
-	char *pathname;
+	if (!sb->s_qcop->quota_on && !sb->s_qcop->quota_on_meta)
-	int ret = -ENOSYS;
+		return -ENOSYS;
-
+	if (sb->s_qcop->quota_on_meta)
-	pathname = getname(addr);
+		return sb->s_qcop->quota_on_meta(sb, type, id);
-	if (IS_ERR(pathname))
+	if (IS_ERR(path))
-		return PTR_ERR(pathname);
+		return PTR_ERR(path);
-	if (sb->s_qcop->quota_on)
+	return sb->s_qcop->quota_on(sb, type, id, path);
-		ret = sb->s_qcop->quota_on(sb, type, id, pathname);
-	putname(pathname);
-	return ret;
 }
 
 static int quota_getfmt(struct super_block *sb, int type, void __user *addr)
@@ -241,7 +238,7 @@ static int quota_getxquota(struct super_block *sb, int type, qid_t id,
 
 /* Copy parameters and call proper function */
 static int do_quotactl(struct super_block *sb, int type, int cmd, qid_t id,
-		       void __user *addr)
+		       void __user *addr, struct path *path)
 {
 	int ret;
 
@@ -256,7 +253,7 @@ static int do_quotactl(struct super_block *sb, int type, int cmd, qid_t id,
 
 	switch (cmd) {
 	case Q_QUOTAON:
-		return quota_quotaon(sb, type, cmd, id, addr);
+		return quota_quotaon(sb, type, cmd, id, path);
 	case Q_QUOTAOFF:
 		if (!sb->s_qcop->quota_off)
 			return -ENOSYS;
@@ -335,6 +332,7 @@ SYSCALL_DEFINE4(quotactl, unsigned int, cmd, const char __user *, special,
 {
 	uint cmds, type;
 	struct super_block *sb = NULL;
+	struct path path, *pathp = NULL;
 	int ret;
 
 	cmds = cmd >> SUBCMDSHIFT;
@@ -351,12 +349,27 @@ SYSCALL_DEFINE4(quotactl, unsigned int, cmd, const char __user *, special,
 		return -ENODEV;
 	}
 
+	/*
+	 * Path for quotaon has to be resolved before grabbing superblock
+	 * because that gets s_umount sem which is also possibly needed by path
+	 * resolution (think about autofs) and thus deadlocks could arise.
+	 */
+	if (cmds == Q_QUOTAON) {
+		ret = user_path_at(AT_FDCWD, addr, LOOKUP_FOLLOW, &path);
+		if (ret)
+			pathp = ERR_PTR(ret);
+		else
+			pathp = &path;
+	}
+
 	sb = quotactl_block(special);
 	if (IS_ERR(sb))
 		return PTR_ERR(sb);
 
-	ret = do_quotactl(sb, type, cmds, id, addr);
+	ret = do_quotactl(sb, type, cmds, id, addr, pathp);
 
 	drop_super(sb);
+	if (pathp && !IS_ERR(pathp))
+		path_put(pathp);
 	return ret;
 }

fs/reiserfs/super.c

@@ -632,7 +632,7 @@ static int reiserfs_acquire_dquot(struct dquot *);
 static int reiserfs_release_dquot(struct dquot *);
 static int reiserfs_mark_dquot_dirty(struct dquot *);
 static int reiserfs_write_info(struct super_block *, int);
-static int reiserfs_quota_on(struct super_block *, int, int, char *);
+static int reiserfs_quota_on(struct super_block *, int, int, struct path *);
 
 static const struct dquot_operations reiserfs_quota_operations = {
 	.write_dquot = reiserfs_write_dquot,
@@ -2048,25 +2048,21 @@ static int reiserfs_quota_on_mount(struct super_block *sb, int type)
  * Standard function to be called on quota_on
  */
 static int reiserfs_quota_on(struct super_block *sb, int type, int format_id,
-			     char *name)
+			     struct path *path)
 {
 	int err;
-	struct path path;
 	struct inode *inode;
 	struct reiserfs_transaction_handle th;
 
 	if (!(REISERFS_SB(sb)->s_mount_opt & (1 << REISERFS_QUOTA)))
 		return -EINVAL;
 
-	err = kern_path(name, LOOKUP_FOLLOW, &path);
-	if (err)
-		return err;
 	/* Quotafile not on the same filesystem? */
-	if (path.mnt->mnt_sb != sb) {
+	if (path->mnt->mnt_sb != sb) {
 		err = -EXDEV;
 		goto out;
 	}
-	inode = path.dentry->d_inode;
+	inode = path->dentry->d_inode;
 	/* We must not pack tails for quota files on reiserfs for quota IO to work */
 	if (!(REISERFS_I(inode)->i_flags & i_nopack_mask)) {
 		err = reiserfs_unpack(inode, NULL);
@@ -2082,7 +2078,7 @@ static int reiserfs_quota_on(struct super_block *sb, int type, int format_id,
 	/* Journaling quota? */
 	if (REISERFS_SB(sb)->s_qf_names[type]) {
 		/* Quotafile not of fs root? */
-		if (path.dentry->d_parent != sb->s_root)
+		if (path->dentry->d_parent != sb->s_root)
 			reiserfs_warning(sb, "super-6521",
 				 "Quota file not on filesystem root. "
 				 "Journalled quota will not work.");
@@ -2101,9 +2097,8 @@ static int reiserfs_quota_on(struct super_block *sb, int type, int format_id,
 		if (err)
 			goto out;
 	}
-	err = dquot_quota_on_path(sb, type, format_id, &path);
+	err = dquot_quota_on(sb, type, format_id, path);
 out:
-	path_put(&path);
 	return err;
 }
 

include/linux/quota.h

@@ -322,9 +322,12 @@ struct dquot_operations {
 	qsize_t *(*get_reserved_space) (struct inode *);
 };
 
+struct path;
+
 /* Operations handling requests from userspace */
 struct quotactl_ops {
-	int (*quota_on)(struct super_block *, int, int, char *);
+	int (*quota_on)(struct super_block *, int, int, struct path *);
+	int (*quota_on_meta)(struct super_block *, int, int);
 	int (*quota_off)(struct super_block *, int);
 	int (*quota_sync)(struct super_block *, int, int);
 	int (*get_info)(struct super_block *, int, struct if_dqinfo *);

include/linux/quotaops.h

@@ -76,11 +76,9 @@ int dquot_mark_dquot_dirty(struct dquot *dquot);
 
 int dquot_file_open(struct inode *inode, struct file *file);
 
-int dquot_quota_on(struct super_block *sb, int type, int format_id,
-	char *path);
 int dquot_enable(struct inode *inode, int type, int format_id,
 	unsigned int flags);
-int dquot_quota_on_path(struct super_block *sb, int type, int format_id,
+int dquot_quota_on(struct super_block *sb, int type, int format_id,
  	struct path *path);
 int dquot_quota_on_mount(struct super_block *sb, char *qf_name,
  	int format_id, int type);