From: Pavel Emelyanov This flag tells the .get_sb callback that this is a kern_mount() call so that it can trust *data pointer to be valid in-kernel one. If this flag is passed from the user process, it is cleared since the *data pointer is not a valid kernel object. Running a few steps forward - this will be needed for proc to create the superblock and store a valid pid namespace on it during the namespace creation. The reason, why the namespace cannot live without proc mount is described in the appropriate patch. Signed-off-by: Pavel Emelyanov Cc: Oleg Nesterov Cc: Sukadev Bhattiprolu Cc: Paul Menage Cc: "Eric W. Biederman" Signed-off-by: Andrew Morton --- fs/namespace.c | 3 ++- fs/super.c | 6 +++--- include/linux/fs.h | 4 +++- 3 files changed, 8 insertions(+), 5 deletions(-) diff -puN fs/namespace.c~pid-namespaces-introduce-ms_kernmount-flag fs/namespace.c --- a/fs/namespace.c~pid-namespaces-introduce-ms_kernmount-flag +++ a/fs/namespace.c @@ -1605,7 +1605,8 @@ long do_mount(char *dev_name, char *dir_ mnt_flags |= MNT_NOMNT; flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE | - MS_NOATIME | MS_NODIRATIME | MS_RELATIME | MS_NOMNT); + MS_NOATIME | MS_NODIRATIME | MS_RELATIME | + MS_NOMNT | MS_KERNMOUNT); /* ... and get the mountpoint */ retval = path_lookup(dir_name, LOOKUP_FOLLOW, &nd); diff -puN fs/super.c~pid-namespaces-introduce-ms_kernmount-flag fs/super.c --- a/fs/super.c~pid-namespaces-introduce-ms_kernmount-flag +++ a/fs/super.c @@ -918,9 +918,9 @@ do_kern_mount(const char *fstype, int fl return mnt; } -struct vfsmount *kern_mount(struct file_system_type *type) +struct vfsmount *kern_mount_data(struct file_system_type *type, void *data) { - return vfs_kern_mount(type, 0, type->name, NULL); + return vfs_kern_mount(type, MS_KERNMOUNT, type->name, data); } -EXPORT_SYMBOL(kern_mount); +EXPORT_SYMBOL_GPL(kern_mount_data); diff -puN include/linux/fs.h~pid-namespaces-introduce-ms_kernmount-flag include/linux/fs.h --- a/include/linux/fs.h~pid-namespaces-introduce-ms_kernmount-flag +++ a/include/linux/fs.h @@ -129,6 +129,7 @@ extern int dir_notify_enable; #define MS_RELATIME (1<<21) /* Update atime relative to mtime/ctime. */ #define MS_SETUSER (1<<23) /* set mnt_uid to current user */ #define MS_NOMNT (1<<24) /* don't allow unprivileged submounts */ +#define MS_KERNMOUNT (1<<25) /* this is a kern_mount call */ #define MS_ACTIVE (1<<30) #define MS_NOUSER (1<<31) @@ -1458,7 +1459,8 @@ void unnamed_dev_init(void); extern int register_filesystem(struct file_system_type *); extern int unregister_filesystem(struct file_system_type *); -extern struct vfsmount *kern_mount(struct file_system_type *); +extern struct vfsmount *kern_mount_data(struct file_system_type *, void *data); +#define kern_mount(type) kern_mount_data(type, NULL) extern int may_umount_tree(struct vfsmount *); extern int may_umount(struct vfsmount *); extern void umount_tree(struct vfsmount *, int, struct list_head *); _