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Commit f9bd6733 authored by Eric W. Biederman's avatar Eric W. Biederman
Browse files

sysctl: Allow creating permanently empty directories that serve as mountpoints. 



Add a magic sysctl table sysctl_mount_point that when used to
create a directory forces that directory to be permanently empty.

Update the code to use make_empty_dir_inode when accessing permanently
empty directories.

Update the code to not allow adding to permanently empty directories.

Update /proc/sys/fs/binfmt_misc to be a permanently empty directory.

Cc: stable@vger.kernel.org
Signed-off-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
parent fbabfd0f

fs/proc/proc_sysctl.c

+37 −0
Original line number Diff line number Diff line
@@ -19,6 +19,28 @@ static const struct inode_operations proc_sys_inode_operations; 
static const struct file_operations proc_sys_dir_file_operations;

static const struct inode_operations proc_sys_dir_operations;



/* Support for permanently empty directories */



struct ctl_table sysctl_mount_point[] = {

	{ }

};



static bool is_empty_dir(struct ctl_table_header *head)

{

	return head->ctl_table[0].child == sysctl_mount_point;

}



static void set_empty_dir(struct ctl_dir *dir)

{

	dir->header.ctl_table[0].child = sysctl_mount_point;

}



static void clear_empty_dir(struct ctl_dir *dir)



{

	dir->header.ctl_table[0].child = NULL;

}



void proc_sys_poll_notify(struct ctl_table_poll *poll)

{

	if (!poll)
@@ -187,6 +209,17 @@ static int insert_header(struct ctl_dir *dir, struct ctl_table_header *header) 
	struct ctl_table *entry;

	int err;



	/* Is this a permanently empty directory? */

	if (is_empty_dir(&dir->header))

		return -EROFS;



	/* Am I creating a permanently empty directory? */

	if (header->ctl_table == sysctl_mount_point) {

		if (!RB_EMPTY_ROOT(&dir->root))

			return -EINVAL;

		set_empty_dir(dir);

	}



	dir->header.nreg++;

	header->parent = dir;

	err = insert_links(header);
@@ -202,6 +235,8 @@ static int insert_header(struct ctl_dir *dir, struct ctl_table_header *header) 
	erase_header(header);

	put_links(header);

fail_links:

	if (header->ctl_table == sysctl_mount_point)

		clear_empty_dir(dir);

	header->parent = NULL;

	drop_sysctl_table(&dir->header);

	return err;
@@ -419,6 +454,8 @@ static struct inode *proc_sys_make_inode(struct super_block *sb, 
		inode->i_mode |= S_IFDIR;

		inode->i_op = &proc_sys_dir_operations;

		inode->i_fop = &proc_sys_dir_file_operations;

		if (is_empty_dir(head))

			make_empty_dir_inode(inode);

	}

out:

	return inode;

include/linux/sysctl.h

+3 −0
Original line number Diff line number Diff line
@@ -188,6 +188,9 @@ struct ctl_table_header *register_sysctl_paths(const struct ctl_path *path, 
void unregister_sysctl_table(struct ctl_table_header * table);



extern int sysctl_init(void);



extern struct ctl_table sysctl_mount_point[];



#else /* CONFIG_SYSCTL */

static inline struct ctl_table_header *register_sysctl_table(struct ctl_table * table)

{

kernel/sysctl.c

+1 −7
Original line number Diff line number Diff line
@@ -1531,12 +1531,6 @@ static struct ctl_table vm_table[] = { 
	{ }

};



#if defined(CONFIG_BINFMT_MISC) || defined(CONFIG_BINFMT_MISC_MODULE)

static struct ctl_table binfmt_misc_table[] = {

	{ }

};

#endif



static struct ctl_table fs_table[] = {

	{

		.procname	= "inode-nr",
@@ -1690,7 +1684,7 @@ static struct ctl_table fs_table[] = { 
	{

		.procname	= "binfmt_misc",

		.mode		= 0555,

		.child		= binfmt_misc_table,

		.child		= sysctl_mount_point,

	},

#endif

	{