[PATCH 26/30] cr: mount namespace

[PATCH 26/30] cr: mount namespace

[Alexey Dobriyan]

This is one big FIXME:
	What to do with overmounted files?
	What to do with mounts at all, who should restore them?

just restore something to not oops on task exit

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---

 fs/namespace.c                |   22 ++++++--
 include/linux/cr.h            |    6 ++
 include/linux/mnt_namespace.h |    1 
 kernel/cr/Makefile            |    1 
 kernel/cr/cpt-sys.c           |    6 ++
 kernel/cr/cr-mnt.c            |  108 ++++++++++++++++++++++++++++++++++++++++++
 kernel/cr/cr-nsproxy.c        |    2 
 kernel/cr/cr.h                |    4 +
 8 files changed, 144 insertions(+), 6 deletions(-)

--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1970,6 +1970,21 @@ dput_out:
 	return retval;
 }
 
+struct mnt_namespace *alloc_mnt_ns(void)
+{
+	struct mnt_namespace *mnt_ns;
+
+	mnt_ns = kmalloc(sizeof(struct mnt_namespace), GFP_KERNEL);
+	if (mnt_ns) {
+		atomic_set(&mnt_ns->count, 1);
+		mnt_ns->root = NULL;
+		INIT_LIST_HEAD(&mnt_ns->list);
+		init_waitqueue_head(&mnt_ns->poll);
+		mnt_ns->event = 0;
+	}
+	return mnt_ns;
+}
+
 /*
  * Allocate a new namespace structure and populate it with contents
  * copied from the namespace of the passed in task structure.
@@ -1981,15 +1996,10 @@ static struct mnt_namespace *dup_mnt_ns(struct mnt_namespace *mnt_ns,
 	struct vfsmount *rootmnt = NULL, *pwdmnt = NULL;
 	struct vfsmount *p, *q;
 
-	new_ns = kmalloc(sizeof(struct mnt_namespace), GFP_KERNEL);
+	new_ns = alloc_mnt_ns();
 	if (!new_ns)
 		return ERR_PTR(-ENOMEM);
 
-	atomic_set(&new_ns->count, 1);
-	INIT_LIST_HEAD(&new_ns->list);
-	init_waitqueue_head(&new_ns->poll);
-	new_ns->event = 0;
-
 	down_write(&namespace_sem);
 	/* First pass: copy the tree topology */
 	new_ns->root = copy_tree(mnt_ns->root, mnt_ns->root->mnt_root,
--- a/include/linux/cr.h
+++ b/include/linux/cr.h
@@ -48,6 +48,7 @@ struct cr_object_header {
 #define CR_OBJ_GROUP_INFO	17
 #define CR_OBJ_USER_STRUCT	18
 #define CR_OBJ_USER_NS		19
+#define CR_OBJ_MNT_NS		20
 	__u32	cr_type;	/* object type */
 	__u32	cr_len;		/* object length in bytes including header */
 } __packed;
@@ -176,6 +177,7 @@ struct cr_image_nsproxy {
 	struct cr_object_header cr_hdr;
 
 	cr_pos_t	cr_pos_uts_ns;
+	cr_pos_t	cr_pos_mnt_ns;
 	cr_pos_t	cr_pos_pid_ns;
 } __packed;
 
@@ -190,6 +192,10 @@ struct cr_image_uts_ns {
 	__u8		cr_domainname[64];
 } __packed;
 
+struct cr_image_mnt_ns {
+	struct cr_object_header cr_hdr;
+} __packed;
+
 struct cr_image_pid_ns {
 	struct cr_object_header cr_hdr;
 
--- a/include/linux/mnt_namespace.h
+++ b/include/linux/mnt_namespace.h
@@ -24,6 +24,7 @@ struct proc_mounts {
 
 struct fs_struct;
 
+struct mnt_namespace *alloc_mnt_ns(void);
 extern struct mnt_namespace *copy_mnt_ns(unsigned long, struct mnt_namespace *,
 		struct fs_struct *);
 extern void __put_mnt_ns(struct mnt_namespace *ns);
--- a/kernel/cr/Makefile
+++ b/kernel/cr/Makefile
@@ -5,6 +5,7 @@ cr-y += cr-cred.o
 cr-y += cr-file.o
 cr-y += cr-fs.o
 cr-y += cr-mm.o
+cr-y += cr-mnt.o
 cr-y += cr-nsproxy.o
 cr-y += cr-pid.o
 cr-y += cr-signal.o
--- a/kernel/cr/cpt-sys.c
+++ b/kernel/cr/cpt-sys.c
@@ -71,6 +71,9 @@ static int cr_collect(struct cr_context *ctx)
 	rv = cr_collect_all_uts_ns(ctx);
 	if (rv < 0)
 		return rv;
+	rv = cr_collect_all_mnt_ns(ctx);
+	if (rv < 0)
+		return rv;
 	rv = cr_collect_all_pid_ns(ctx);
 	if (rv < 0)
 		return rv;
@@ -158,6 +161,9 @@ static int cr_dump(struct cr_context *ctx)
 	rv = cr_dump_all_cred(ctx);
 	if (rv < 0)
 		return rv;
+	rv = cr_dump_all_mnt_ns(ctx);
+	if (rv < 0)
+		return rv;
 	rv = cr_dump_all_file(ctx);
 	if (rv < 0)
 		return rv;
new file mode 100644
--- /dev/null
+++ b/kernel/cr/cr-mnt.c
@@ -0,0 +1,108 @@
+/* Copyright (C) 2000-2009 Parallels Holdings, Ltd. */
+#include <linux/fs.h>
+#include <linux/mnt_namespace.h>
+
+#include <linux/cr.h>
+#include "cr.h"
+
+static int cr_collect_mnt_ns(struct cr_context *ctx, struct mnt_namespace *mnt_ns)
+{
+	int rv;
+
+	rv = cr_collect_object(ctx, mnt_ns, CR_CTX_MNT_NS);
+	printk("collect mnt_ns %p: rv %d\n", mnt_ns, rv);
+	return rv;
+}
+
+int cr_collect_all_mnt_ns(struct cr_context *ctx)
+{
+	struct cr_object *obj;
+	int rv;
+
+	for_each_cr_object(ctx, obj, CR_CTX_NSPROXY) {
+		struct nsproxy *nsproxy = obj->o_obj;
+
+		rv = cr_collect_mnt_ns(ctx, nsproxy->mnt_ns);
+		if (rv < 0)
+			return rv;
+	}
+	for_each_cr_object(ctx, obj, CR_CTX_MNT_NS) {
+		struct mnt_namespace *mnt_ns = obj->o_obj;
+		unsigned int cnt = atomic_read(&mnt_ns->count);
+
+		if (obj->o_count != cnt) {
+			printk("%s: mnt_ns %p has external references %lu:%u\n", __func__, mnt_ns, obj->o_count, cnt);
+			return -EINVAL;
+		}
+	}
+	return 0;
+}
+
+static int cr_dump_mnt_ns(struct cr_context *ctx, struct cr_object *obj)
+{
+	struct mnt_namespace *mnt_ns = obj->o_obj;
+	struct cr_image_mnt_ns *i;
+	int rv;
+
+	printk("dump mnt_ns %p\n", mnt_ns);
+
+	i = cr_prepare_image(CR_OBJ_MNT_NS, sizeof(*i));
+	if (!i)
+		return -ENOMEM;
+
+	obj->o_pos = ctx->cr_dump_file->f_pos;
+	rv = cr_write(ctx, i, sizeof(*i));
+	kfree(i);
+	return rv;
+}
+
+int cr_dump_all_mnt_ns(struct cr_context *ctx)
+{
+	struct cr_object *obj;
+	int rv;
+
+	for_each_cr_object(ctx, obj, CR_CTX_MNT_NS) {
+		rv = cr_dump_mnt_ns(ctx, obj);
+		if (rv < 0)
+			return rv;
+	}
+	return 0;
+}
+
+int cr_restore_mnt_ns(struct cr_context *ctx, loff_t pos)
+{
+	struct cr_image_mnt_ns *i;
+	struct mnt_namespace *mnt_ns;
+	struct cr_object *obj;
+	int rv;
+
+	i = kzalloc(sizeof(*i), GFP_KERNEL);
+	if (!i)
+		return -ENOMEM;
+	rv = cr_pread(ctx, i, sizeof(*i), pos);
+	if (rv < 0) {
+		kfree(i);
+		return rv;
+	}
+	if (i->cr_hdr.cr_type != CR_OBJ_MNT_NS) {
+		kfree(i);
+		return -EINVAL;
+	}
+
+	mnt_ns = alloc_mnt_ns();
+	if (!mnt_ns) {
+		kfree(i);
+		return -ENOMEM;
+	}
+	kfree(i);
+
+	obj = cr_object_create(mnt_ns);
+	if (!obj) {
+		kfree(mnt_ns);
+		return -ENOMEM;
+	}
+	obj->o_pos = pos;
+	list_add(&obj->o_list, &ctx->cr_obj[CR_CTX_MNT_NS]);
+	printk("restore mnt_ns %p, pos %lld\n", mnt_ns, (long long)pos);
+	return 0;
+}
--- a/kernel/cr/cr-nsproxy.c
+++ b/kernel/cr/cr-nsproxy.c
@@ -59,6 +59,8 @@ static int cr_dump_nsproxy(struct cr_context *ctx, struct cr_object *obj)
 
 	tmp = cr_find_obj_by_ptr(ctx, nsproxy->uts_ns, CR_CTX_UTS_NS);
 	i->cr_pos_uts_ns = tmp->o_pos;
+	tmp = cr_find_obj_by_ptr(ctx, nsproxy->mnt_ns, CR_CTX_MNT_NS);
+	i->cr_pos_mnt_ns = tmp->o_pos;
 	tmp = cr_find_obj_by_ptr(ctx, nsproxy->pid_ns, CR_CTX_PID_NS);
 	i->cr_pos_pid_ns = tmp->o_pos;
 
--- a/kernel/cr/cr.h
+++ b/kernel/cr/cr.h
@@ -28,6 +28,7 @@ enum cr_context_obj_type {
 	CR_CTX_FS_STRUCT,
 	CR_CTX_GROUP_INFO,
 	CR_CTX_MM_STRUCT,
+	CR_CTX_MNT_NS,
 	CR_CTX_NSPROXY,
 	CR_CTX_PID,
 	CR_CTX_PID_NS,
@@ -95,6 +96,7 @@ int cr_collect_all_file(struct cr_context *ctx);
 int cr_collect_all_fs_struct(struct cr_context *ctx);
 int cr_collect_all_group_info(struct cr_context *ctx);
 int cr_collect_all_mm_struct(struct cr_context *ctx);
+int cr_collect_all_mnt_ns(struct cr_context *ctx);
 int cr_collect_all_nsproxy(struct cr_context *ctx);
 int cr_collect_all_pid_ns(struct cr_context *ctx);
 int cr_collect_all_pid(struct cr_context *ctx);
@@ -111,6 +113,7 @@ int cr_dump_all_file(struct cr_context *ctx);
 int cr_dump_all_fs_struct(struct cr_context *ctx);
 int cr_dump_all_group_info(struct cr_context *ctx);
 int cr_dump_all_mm_struct(struct cr_context *ctx);
+int cr_dump_all_mnt_ns(struct cr_context *ctx);
 int cr_dump_all_nsproxy(struct cr_context *ctx);
 int cr_dump_all_pid_ns(struct cr_context *ctx);
 int cr_dump_all_pid(struct cr_context *ctx);
@@ -127,6 +130,7 @@ int cr_restore_file(struct cr_context *ctx, loff_t pos);
 int cr_restore_fs_struct(struct cr_context *ctx, loff_t pos);
 int cr_restore_group_info(struct cr_context *ctx, loff_t pos);
 int cr_restore_mm_struct(struct cr_context *ctx, loff_t pos);
+int cr_restore_mnt_ns(struct cr_context *ctx, loff_t pos);
 int cr_restore_nsproxy(struct cr_context *ctx, loff_t pos);
 int cr_restore_pid_ns(struct cr_context *ctx, loff_t pos);
 int cr_restore_pid(struct cr_context *ctx, struct cr_image_task_struct *i);

Re: [PATCH 26/30] cr: mount namespace

[Dave Hansen]

On Fri, 2009-04-10 at 06:40 +0400, Alexey Dobriyan wrote:
> 
> +struct mnt_namespace *alloc_mnt_ns(void)
> +{
> +       struct mnt_namespace *mnt_ns;
> +
> +       mnt_ns = kmalloc(sizeof(struct mnt_namespace), GFP_KERNEL);
> +       if (mnt_ns) {
> +               atomic_set(&mnt_ns->count, 1);
> +               mnt_ns->root = NULL;
> +               INIT_LIST_HEAD(&mnt_ns->list);
> +               init_waitqueue_head(&mnt_ns->poll);
> +               mnt_ns->event = 0;
> +       }
> +       return mnt_ns;
> +}
> +
>  /*
>   * Allocate a new namespace structure and populate it with contents
>   * copied from the namespace of the passed in task structure.
> @@ -1981,15 +1996,10 @@ static struct mnt_namespace *dup_mnt_ns(struct
> mnt_namespace *mnt_ns,
>         struct vfsmount *rootmnt = NULL, *pwdmnt = NULL;
>         struct vfsmount *p, *q;
> 
> -       new_ns = kmalloc(sizeof(struct mnt_namespace), GFP_KERNEL);
> +       new_ns = alloc_mnt_ns();
>         if (!new_ns)
>                 return ERR_PTR(-ENOMEM);
> 
> -       atomic_set(&new_ns->count, 1);
> -       INIT_LIST_HEAD(&new_ns->list);
> -       init_waitqueue_head(&new_ns->poll);
> -       new_ns->event = 0;
> -
>         down_write(&namespace_sem);
>         /* First pass: copy the tree topology */
>         new_ns->root = copy_tree(mnt_ns->root, mnt_ns->root->mnt_root,
> --- a/include/linux/cr.h

This bit should be broken out, and stuck at the beginning of the series.

-- Dave

Re: [PATCH 26/30] cr: mount namespace

[Dave Hansen]

On Fri, 2009-04-10 at 06:40 +0400, Alexey Dobriyan wrote:
> +int cr_collect_all_mnt_ns(struct cr_context *ctx)
> +{
> +       struct cr_object *obj;
> +       int rv;
> +
> +       for_each_cr_object(ctx, obj, CR_CTX_NSPROXY) {
> +               struct nsproxy *nsproxy = obj->o_obj;
> +
> +               rv = cr_collect_mnt_ns(ctx, nsproxy->mnt_ns);
> +               if (rv < 0)
> +                       return rv;
> +       }
> +       for_each_cr_object(ctx, obj, CR_CTX_MNT_NS) {
> +               struct mnt_namespace *mnt_ns = obj->o_obj;
> +               unsigned int cnt = atomic_read(&mnt_ns->count);
> +
> +               if (obj->o_count != cnt) {
> +                       printk("%s: mnt_ns %p has external references %lu:%u\n", __func__, mnt_ns, obj->o_count, cnt);
> +                       return -EINVAL;
> +               }
> +       }
> +       return 0;
> +}

I worry about depending on refcounts like this, especially when
userspace has an interface that can elevate them.  If someone is holding
open /proc/$pid/mounts, this will get elevated and trip the check.  This
check is also naturally racy.  You check once if there are references,
but there is no locking to keep new references from coming in.  

That said, I do like how this for_each_cr_object() stuff looks.  It's
pretty clean.

-- Dave