[CFT][PATCH 05/10] sysctl: Allow creating permanently empty directories that serve as mountpoints.
From: Eric W. Biederman <hidden>
Date: 2015-05-16 02:08:27
Also in:
linux-fsdevel
Subsystem:
filesystems (vfs and infrastructure), proc filesystem, proc sysctl, the rest · Maintainers:
Alexander Viro, Christian Brauner, Kees Cook, Joel Granados, Linus Torvalds
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-u79uwXL29TY76Z2rM5mHXA@public.gmane.org Signed-off-by: "Eric W. Biederman" <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org> --- fs/proc/proc_sysctl.c | 37 +++++++++++++++++++++++++++++++++++++ include/linux/sysctl.h | 3 +++ kernel/sysctl.c | 8 +------- 3 files changed, 41 insertions(+), 7 deletions(-)
diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index fea2561d773b..fdda62e6115e 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c@@ -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 @@ 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(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;
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 795d5fea5697..fa7bc29925c9 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h@@ -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) {
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 2082b1a88fb9..c3eee4c6d6c1 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c@@ -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 {
--
2.2.1