Commit 8d0347f6 authored by David Howells's avatar David Howells Committed by Al Viro
Browse files

convert do_remount_sb() to fs_context 



Replace do_remount_sb() with a function, reconfigure_super(), that's
fs_context aware.  The fs_context is expected to be parameterised already
and have ->root pointing to the superblock to be reconfigured.

A legacy wrapper is provided that is intended to be called from the
fs_context ops when those appear, but for now is called directly from
reconfigure_super().  This wrapper invokes the ->remount_fs() superblock op
for the moment.  It is intended that the remount_fs() op will be phased
out.

The fs_context->purpose is set to FS_CONTEXT_FOR_RECONFIGURE to indicate
that the context is being used for reconfiguration.

do_umount_root() is provided to consolidate remount-to-R/O for umount and
emergency remount by creating a context and invoking reconfiguration.

do_remount(), do_umount() and do_emergency_remount_callback() are switched
to use the new process.

[AV -- fold UMOUNT and EMERGENCY_REMOUNT in; fixes the
umount / bug, gets rid of pointless complexity]
[AV -- set ->net_ns in all cases; nfs remount will need that]
[AV -- shift security_sb_remount() call into reconfigure_super(); the callers
that didn't do security_sb_remount() have NULL fc->security anyway, so it's
a no-op for them]

Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
Co-developed-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent c9ce29ed

fs/fs_context.c

+33 −2
Original line number Diff line number Diff line
@@ -69,6 +69,13 @@ static struct fs_context *alloc_fs_context(struct file_system_type *fs_type, 
	case FS_CONTEXT_FOR_MOUNT:

		fc->user_ns = get_user_ns(fc->cred->user_ns);

		break;

	case FS_CONTEXT_FOR_RECONFIGURE:

		/* We don't pin any namespaces as the superblock's

		 * subscriptions cannot be changed at this point.

		 */

		atomic_inc(&reference->d_sb->s_active);

		fc->root = dget(reference);

		break;

	}



	ret = legacy_init_fs_context(fc);
@@ -90,6 +97,15 @@ struct fs_context *fs_context_for_mount(struct file_system_type *fs_type, 
}

EXPORT_SYMBOL(fs_context_for_mount);



struct fs_context *fs_context_for_reconfigure(struct dentry *dentry,

					unsigned int sb_flags,

					unsigned int sb_flags_mask)

{

	return alloc_fs_context(dentry->d_sb->s_type, dentry, sb_flags,

				sb_flags_mask, FS_CONTEXT_FOR_RECONFIGURE);

}

EXPORT_SYMBOL(fs_context_for_reconfigure);



void fc_drop_locked(struct fs_context *fc)

{

	struct super_block *sb = fc->root->d_sb;
@@ -99,6 +115,7 @@ void fc_drop_locked(struct fs_context *fc) 
}



static void legacy_fs_context_free(struct fs_context *fc);



/**

 * put_fs_context - Dispose of a superblock configuration context.

 * @fc: The context to dispose of.
@@ -118,7 +135,6 @@ void put_fs_context(struct fs_context *fc) 
		legacy_fs_context_free(fc);



	security_free_mnt_opts(&fc->security);

	if (fc->net_ns)

	put_net(fc->net_ns);

	put_user_ns(fc->user_ns);

	put_cred(fc->cred);
@@ -172,6 +188,21 @@ int legacy_get_tree(struct fs_context *fc) 
	return 0;

}



/*

 * Handle remount.

 */

int legacy_reconfigure(struct fs_context *fc)

{

	struct legacy_fs_context *ctx = fc->fs_private;

	struct super_block *sb = fc->root->d_sb;



	if (!sb->s_op->remount_fs)

		return 0;



	return sb->s_op->remount_fs(sb, &fc->sb_flags,

				    ctx ? ctx->legacy_data : NULL);

}



/*

 * Initialise a legacy context for a filesystem that doesn't support

 * fs_context.

fs/internal.h

+2 −1
Original line number Diff line number Diff line
@@ -56,6 +56,7 @@ extern void __init chrdev_init(void); 
 * fs_context.c

 */

extern int legacy_get_tree(struct fs_context *fc);

extern int legacy_reconfigure(struct fs_context *fc);

extern int parse_monolithic_mount_data(struct fs_context *, void *);

extern void fc_drop_locked(struct fs_context *);
@@ -107,7 +108,7 @@ extern struct file *alloc_empty_file_noaccount(int, const struct cred *); 
/*

 * super.c

 */

extern int do_remount_sb(struct super_block *, int, void *, int);

extern int reconfigure_super(struct fs_context *);

extern bool trylock_super(struct super_block *sb);

extern struct super_block *user_get_super(dev_t);

fs/namespace.c

+39 −22
Original line number Diff line number Diff line
@@ -1489,6 +1489,29 @@ static void umount_tree(struct mount *mnt, enum umount_tree_flags how) 


static void shrink_submounts(struct mount *mnt);



static int do_umount_root(struct super_block *sb)

{

	int ret = 0;



	down_write(&sb->s_umount);

	if (!sb_rdonly(sb)) {

		struct fs_context *fc;



		fc = fs_context_for_reconfigure(sb->s_root, SB_RDONLY,

						SB_RDONLY);

		if (IS_ERR(fc)) {

			ret = PTR_ERR(fc);

		} else {

			ret = parse_monolithic_mount_data(fc, NULL);

			if (!ret)

				ret = reconfigure_super(fc);

			put_fs_context(fc);

		}

	}

	up_write(&sb->s_umount);

	return ret;

}



static int do_umount(struct mount *mnt, int flags)

{

	struct super_block *sb = mnt->mnt.mnt_sb;
@@ -1554,11 +1577,7 @@ static int do_umount(struct mount *mnt, int flags) 
		 */

		if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN))

			return -EPERM;

		down_write(&sb->s_umount);

		if (!sb_rdonly(sb))

			retval = do_remount_sb(sb, SB_RDONLY, NULL, 0);

		up_write(&sb->s_umount);

		return retval;

		return do_umount_root(sb);

	}



	namespace_lock();
@@ -2367,7 +2386,7 @@ static int do_remount(struct path *path, int ms_flags, int sb_flags, 
	int err;

	struct super_block *sb = path->mnt->mnt_sb;

	struct mount *mnt = real_mount(path->mnt);

	void *sec_opts = NULL;

	struct fs_context *fc;



	if (!check_mnt(mnt))

		return -EINVAL;
@@ -2378,24 +2397,22 @@ static int do_remount(struct path *path, int ms_flags, int sb_flags, 
	if (!can_change_locked_flags(mnt, mnt_flags))

		return -EPERM;



	if (data && !(sb->s_type->fs_flags & FS_BINARY_MOUNTDATA)) {

		err = security_sb_eat_lsm_opts(data, &sec_opts);

		if (err)

			return err;

	}

	err = security_sb_remount(sb, sec_opts);

	security_free_mnt_opts(&sec_opts);

	if (err)

		return err;

	fc = fs_context_for_reconfigure(path->dentry, sb_flags, MS_RMT_MASK);

	if (IS_ERR(fc))

		return PTR_ERR(fc);



	err = parse_monolithic_mount_data(fc, data);

	if (!err) {

		down_write(&sb->s_umount);

		err = -EPERM;

		if (ns_capable(sb->s_user_ns, CAP_SYS_ADMIN)) {

		err = do_remount_sb(sb, sb_flags, data, 0);

			err = reconfigure_super(fc);

			if (!err)

				set_mount_attributes(mnt, mnt_flags);

		}

		up_write(&sb->s_umount);

	}

	put_fs_context(fc);

	return err;

}

fs/super.c

+73 −34
Original line number Diff line number Diff line
@@ -836,28 +836,35 @@ rescan: 
}



/**

 *	do_remount_sb - asks filesystem to change mount options.

 *	@sb:	superblock in question

 *	@sb_flags: revised superblock flags

 *	@data:	the rest of options

 *      @force: whether or not to force the change

 * reconfigure_super - asks filesystem to change superblock parameters

 * @fc: The superblock and configuration

 *

 *	Alters the mount options of a mounted file system.

 * Alters the configuration parameters of a live superblock.

 */

int do_remount_sb(struct super_block *sb, int sb_flags, void *data, int force)

int reconfigure_super(struct fs_context *fc)

{

	struct super_block *sb = fc->root->d_sb;

	int retval;

	int remount_ro;

	bool remount_ro = false;

	bool force = fc->sb_flags & SB_FORCE;



	if (fc->sb_flags_mask & ~MS_RMT_MASK)

		return -EINVAL;

	if (sb->s_writers.frozen != SB_UNFROZEN)

		return -EBUSY;



	retval = security_sb_remount(sb, fc->security);

	if (retval)

		return retval;



	if (fc->sb_flags_mask & SB_RDONLY) {

#ifdef CONFIG_BLOCK

	if (!(sb_flags & SB_RDONLY) && bdev_read_only(sb->s_bdev))

		if (!(fc->sb_flags & SB_RDONLY) && bdev_read_only(sb->s_bdev))

			return -EACCES;

#endif



	remount_ro = (sb_flags & SB_RDONLY) && !sb_rdonly(sb);

		remount_ro = (fc->sb_flags & SB_RDONLY) && !sb_rdonly(sb);

	}



	if (remount_ro) {

		if (!hlist_empty(&sb->s_pins)) {
@@ -868,13 +875,14 @@ int do_remount_sb(struct super_block *sb, int sb_flags, void *data, int force) 
				return 0;

			if (sb->s_writers.frozen != SB_UNFROZEN)

				return -EBUSY;

			remount_ro = (sb_flags & SB_RDONLY) && !sb_rdonly(sb);

			remount_ro = !sb_rdonly(sb);

		}

	}

	shrink_dcache_sb(sb);



	/* If we are remounting RDONLY and current sb is read/write,

	   make sure there are no rw files opened */

	/* If we are reconfiguring to RDONLY and current sb is read/write,

	 * make sure there are no files open for writing.

	 */

	if (remount_ro) {

		if (force) {

			sb->s_readonly_remount = 1;
@@ -886,8 +894,7 @@ int do_remount_sb(struct super_block *sb, int sb_flags, void *data, int force) 
		}

	}



	if (sb->s_op->remount_fs) {

		retval = sb->s_op->remount_fs(sb, &sb_flags, data);

	retval = legacy_reconfigure(fc);

	if (retval) {

		if (!force)

			goto cancel_readonly;
@@ -895,8 +902,9 @@ int do_remount_sb(struct super_block *sb, int sb_flags, void *data, int force) 
		WARN(1, "forced remount of a %s fs returned %i\n",

		     sb->s_type->name, retval);

	}

	}

	sb->s_flags = (sb->s_flags & ~MS_RMT_MASK) | (sb_flags & MS_RMT_MASK);



	WRITE_ONCE(sb->s_flags, ((sb->s_flags & ~fc->sb_flags_mask) |

				 (fc->sb_flags & fc->sb_flags_mask)));

	/* Needs to be ordered wrt mnt_is_readonly() */

	smp_wmb();

	sb->s_readonly_remount = 0;
@@ -923,10 +931,15 @@ static void do_emergency_remount_callback(struct super_block *sb) 
	down_write(&sb->s_umount);

	if (sb->s_root && sb->s_bdev && (sb->s_flags & SB_BORN) &&

	    !sb_rdonly(sb)) {

		/*

		 * What lock protects sb->s_flags??

		 */

		do_remount_sb(sb, SB_RDONLY, NULL, 1);

		struct fs_context *fc;



		fc = fs_context_for_reconfigure(sb->s_root,

					SB_RDONLY | SB_FORCE, SB_RDONLY);

		if (!IS_ERR(fc)) {

			if (parse_monolithic_mount_data(fc, NULL) == 0)

				(void)reconfigure_super(fc);

			put_fs_context(fc);

		}

	}

	up_write(&sb->s_umount);

}
@@ -1213,6 +1226,31 @@ struct dentry *mount_nodev(struct file_system_type *fs_type, 
}

EXPORT_SYMBOL(mount_nodev);



static int reconfigure_single(struct super_block *s,

			      int flags, void *data)

{

	struct fs_context *fc;

	int ret;



	/* The caller really need to be passing fc down into mount_single(),

	 * then a chunk of this can be removed.  [Bollocks -- AV]

	 * Better yet, reconfiguration shouldn't happen, but rather the second

	 * mount should be rejected if the parameters are not compatible.

	 */

	fc = fs_context_for_reconfigure(s->s_root, flags, MS_RMT_MASK);

	if (IS_ERR(fc))

		return PTR_ERR(fc);



	ret = parse_monolithic_mount_data(fc, data);

	if (ret < 0)

		goto out;



	ret = reconfigure_super(fc);

out:

	put_fs_context(fc);

	return ret;

}



static int compare_single(struct super_block *s, void *p)

{

	return 1;
@@ -1230,13 +1268,14 @@ struct dentry *mount_single(struct file_system_type *fs_type, 
		return ERR_CAST(s);

	if (!s->s_root) {

		error = fill_super(s, data, flags & SB_SILENT ? 1 : 0);

		if (error) {

			deactivate_locked_super(s);

			return ERR_PTR(error);

		}

		if (!error)

			s->s_flags |= SB_ACTIVE;

	} else {

		do_remount_sb(s, flags, data, 0);

		error = reconfigure_single(s, flags, data);

	}

	if (unlikely(error)) {

		deactivate_locked_super(s);

		return ERR_PTR(error);

	}

	return dget(s->s_root);

}

include/linux/fs.h

+1 −0
Original line number Diff line number Diff line
@@ -1337,6 +1337,7 @@ extern int send_sigurg(struct fown_struct *fown); 


/* These sb flags are internal to the kernel */

#define SB_SUBMOUNT     (1<<26)

#define SB_FORCE    	(1<<27)

#define SB_NOSEC	(1<<28)

#define SB_BORN		(1<<29)

#define SB_ACTIVE	(1<<30)

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