| From f9bd6733d3f11e24f3949becf277507d422ee1eb Mon Sep 17 00:00:00 2001 |
| From: "Eric W. Biederman" <ebiederm@xmission.com> |
| Date: Sat, 9 May 2015 22:09:14 -0500 |
| Subject: sysctl: Allow creating permanently empty directories that serve as mountpoints. |
| |
| From: "Eric W. Biederman" <ebiederm@xmission.com> |
| |
| commit f9bd6733d3f11e24f3949becf277507d422ee1eb upstream. |
| |
| 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. |
| |
| Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| fs/proc/proc_sysctl.c | 37 +++++++++++++++++++++++++++++++++++++ |
| include/linux/sysctl.h | 3 +++ |
| kernel/sysctl.c | 8 +------- |
| 3 files changed, 41 insertions(+), 7 deletions(-) |
| |
| --- a/fs/proc/proc_sysctl.c |
| +++ b/fs/proc/proc_sysctl.c |
| @@ -19,6 +19,28 @@ static const struct inode_operations pro |
| 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 |
| 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 @@ fail: |
| 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 |
| 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; |
| --- a/include/linux/sysctl.h |
| +++ b/include/linux/sysctl.h |
| @@ -188,6 +188,9 @@ struct ctl_table_header *register_sysctl |
| 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) |
| { |
| --- a/kernel/sysctl.c |
| +++ b/kernel/sysctl.c |
| @@ -1510,12 +1510,6 @@ 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", |
| @@ -1669,7 +1663,7 @@ static struct ctl_table fs_table[] = { |
| { |
| .procname = "binfmt_misc", |
| .mode = 0555, |
| - .child = binfmt_misc_table, |
| + .child = sysctl_mount_point, |
| }, |
| #endif |
| { |