[Devel] [PATCH RHEL7 COMMIT] fs: make overlayfs disabled in CT by default

[Vladimir Davydov]

The commit is pushed to "branch-rh7-3.10.0-327.18.2.vz7.14.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-327.18.2.vz7.14.24
------>
commit af1bf9e1a067c1186501ef5415acdb62a33e8c22
Author: Maxim Patlasov <mpatlasov at virtuozzo.com>
Date:   Wed Jul 13 20:52:37 2016 +0400

    fs: make overlayfs disabled in CT by default
    
    Overlayfs is in "TECH PREVIEW" state right now. Letting CT users to freely
    mount and exercise overlayfs, we risk to have the whole node crashed.
    
    Let's disable it for CT users by default. Customers who need it (e.g. to
    run Docker in CT) may enable it like this:
    
    # echo 1 > /proc/sys/fs/experimental_fs_enable
    
    The patch is a temporary (awkward) workaround until we make overlayfs
    production-ready. Then we'll roll back the patch.
    
    https://jira.sw.ru/browse/PSBM-49629
    
    Signed-off-by: Maxim Patlasov <mpatlasov at virtuozzo.com>
    Reviewed-by: Vladimir Davydov <vdavydov at virtuozzo.com>
---
 fs/filesystems.c     | 8 +++++++-
 fs/overlayfs/super.c | 2 +-
 include/linux/fs.h   | 4 ++++
 kernel/sysctl.c      | 7 +++++++
 4 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/fs/filesystems.c b/fs/filesystems.c
index beaba560979f..670d228e9c56 100644
--- a/fs/filesystems.c
+++ b/fs/filesystems.c
@@ -16,6 +16,9 @@
 #include <linux/slab.h>
 #include <asm/uaccess.h>
 
+/* Affects ability of CT users to mount fs marked as FS_EXPERIMENTAL */
+int sysctl_experimental_fs_enable;
+
 /*
  * Handling of filesystem drivers list.
  * Rules:
@@ -219,7 +222,10 @@ int __init get_filesystem_list(char *buf)
 
 static inline bool filesystem_permitted(const struct file_system_type *fs)
 {
-	return ve_is_super(get_exec_env()) || (fs->fs_flags & FS_VIRTUALIZED);
+	return ve_is_super(get_exec_env()) ||
+		(fs->fs_flags & FS_VIRTUALIZED) ||
+		((fs->fs_flags & FS_EXPERIMENTAL) &&
+		 sysctl_experimental_fs_enable);
 }
 
 #ifdef CONFIG_PROC_FS
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index c20cfe977cdf..d5c57b4b5983 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -1129,7 +1129,7 @@ static struct file_system_type ovl_fs_type = {
 	.name		= "overlay",
 	.mount		= ovl_mount,
 	.kill_sb	= kill_anon_super,
-	.fs_flags       = FS_VIRTUALIZED,
+	.fs_flags       = FS_EXPERIMENTAL,
 };
 MODULE_ALIAS_FS("overlay");
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 7203dbadbbf9..f1c3d5be60d8 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -59,6 +59,8 @@ extern struct inodes_stat_t inodes_stat;
 extern int leases_enable, lease_break_time;
 extern int sysctl_protected_symlinks;
 extern int sysctl_protected_hardlinks;
+extern int sysctl_experimental_fs_enable;
+
 
 struct buffer_head;
 typedef int (get_block_t)(struct inode *inode, sector_t iblock,
@@ -2108,6 +2110,8 @@ struct file_system_type {
 #define FS_USERNS_MOUNT		8	/* Can be mounted by userns root */
 #define FS_USERNS_DEV_MOUNT	16 /* A userns mount does not imply MNT_NODEV */
 #define FS_VIRTUALIZED		64	/* Can mount this fstype inside ve */
+#define FS_EXPERIMENTAL		128	/* Ability to mount this fstype inside ve
+					 * is governed by experimental_fs_enable */
 #define FS_HAS_RM_XQUOTA	256	/* KABI: fs has the rm_xquota quota op */
 #define FS_HAS_INVALIDATE_RANGE	512	/* FS has new ->invalidatepage with length arg */
 #define FS_RENAME_DOES_D_MOVE	32768	/* FS will handle d_move() during rename() internally. */
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index c8f7bc34c590..e59dd3be92dd 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1781,6 +1781,13 @@ static struct ctl_table fs_table[] = {
 		.proc_handler	= &pipe_proc_fn,
 		.extra1		= &pipe_min_size,
 	},
+	{
+		.procname	= "experimental_fs_enable",
+		.data		= &sysctl_experimental_fs_enable,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+	},
 	{ }
 };