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vfs: Only support slave subtrees across different user namespaces

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Sharing mount subtress with mount namespaces created by unprivileged
users allows unprivileged mounts created by unprivileged users to
propagate to mount namespaces controlled by privileged users.

Prevent nasty consequences by changing shared subtrees to slave
subtress when an unprivileged users creates a new mount namespace.

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2012-07-31 13:13:04 -07:00
parent 771b137168
commit 7a472ef4be
2 changed files with 9 additions and 3 deletions
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11
fs/namespace.c
View File

@ -786,7 +786,7 @@ static struct mount *clone_mnt(struct mount *old, struct dentry *root,
if (!mnt)
return ERR_PTR(-ENOMEM);
if (flag & (CL_SLAVE | CL_PRIVATE))
if (flag & (CL_SLAVE | CL_PRIVATE | CL_SHARED_TO_SLAVE))
mnt->mnt_group_id = 0; /* not a peer of original */
else
mnt->mnt_group_id = old->mnt_group_id;
@ -807,7 +807,8 @@ static struct mount *clone_mnt(struct mount *old, struct dentry *root,
list_add_tail(&mnt->mnt_instance, &sb->s_mounts);
br_write_unlock(&vfsmount_lock);
if (flag & CL_SLAVE) {
if ((flag & CL_SLAVE) ||
((flag & CL_SHARED_TO_SLAVE) && IS_MNT_SHARED(old))) {
list_add(&mnt->mnt_slave, &old->mnt_slave_list);
mnt->mnt_master = old;
CLEAR_MNT_SHARED(mnt);
@ -2331,6 +2332,7 @@ static struct mnt_namespace *dup_mnt_ns(struct mnt_namespace *mnt_ns,
struct mount *p, *q;
struct mount *old = mnt_ns->root;
struct mount *new;
int copy_flags;
new_ns = alloc_mnt_ns(user_ns);
if (IS_ERR(new_ns))
@ -2338,7 +2340,10 @@ static struct mnt_namespace *dup_mnt_ns(struct mnt_namespace *mnt_ns,
down_write(&namespace_sem);
/* First pass: copy the tree topology */
new = copy_tree(old, old->mnt.mnt_root, CL_COPY_ALL | CL_EXPIRE);
copy_flags = CL_COPY_ALL | CL_EXPIRE;
if (user_ns != mnt_ns->user_ns)
copy_flags |= CL_SHARED_TO_SLAVE;
new = copy_tree(old, old->mnt.mnt_root, copy_flags);
if (IS_ERR(new)) {
up_write(&namespace_sem);
free_mnt_ns(new_ns);

1
fs/pnode.h
View File

@ -22,6 +22,7 @@
#define CL_COPY_ALL 0x04
#define CL_MAKE_SHARED 0x08
#define CL_PRIVATE 0x10
#define CL_SHARED_TO_SLAVE 0x20
static inline void set_mnt_shared(struct mount *mnt)
{