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vfs: Don't copy mount bind mounts of /proc/<pid>/ns/mnt between namespaces

Don't copy bind mounts of /proc/<pid>/ns/mnt between namespaces.
These files hold references to a mount namespace and copying them
between namespaces could result in a reference counting loop.

The current mnt_ns_loop test prevents loops on the assumption that
mounts don't cross between namespaces.  Unfortunately unsharing a
mount namespace and shared substrees can both cause mounts to
propogate between mount namespaces.

Add two flags CL_COPY_UNBINDABLE and CL_COPY_MNT_NS_FILE are added to
control this behavior, and CL_COPY_ALL is redefined as both of them.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
master
Eric W. Biederman 8 years ago
parent
commit
4ce5d2b1a8
  1. 46
      fs/namespace.c
  2. 5
      fs/pnode.h

46
fs/namespace.c

@ -1355,14 +1355,11 @@ SYSCALL_DEFINE1(oldumount, char __user *, name)
#endif
static bool mnt_ns_loop(struct path *path)
static bool is_mnt_ns_file(struct dentry *dentry)
{
/* Could bind mounting the mount namespace inode cause a
* mount namespace loop?
*/
struct inode *inode = path->dentry->d_inode;
/* Is this a proxy for a mount namespace? */
struct inode *inode = dentry->d_inode;
struct proc_ns *ei;
struct mnt_namespace *mnt_ns;
if (!proc_ns_inode(inode))
return false;
@ -1371,7 +1368,19 @@ static bool mnt_ns_loop(struct path *path)
if (ei->ns_ops != &mntns_operations)
return false;
mnt_ns = ei->ns;
return true;
}
static bool mnt_ns_loop(struct dentry *dentry)
{
/* Could bind mounting the mount namespace inode cause a
* mount namespace loop?
*/
struct mnt_namespace *mnt_ns;
if (!is_mnt_ns_file(dentry))
return false;
mnt_ns = get_proc_ns(dentry->d_inode)->ns;
return current->nsproxy->mnt_ns->seq >= mnt_ns->seq;
}
@ -1380,7 +1389,10 @@ struct mount *copy_tree(struct mount *mnt, struct dentry *dentry,
{
struct mount *res, *p, *q, *r, *parent;
if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(mnt))
if (!(flag & CL_COPY_UNBINDABLE) && IS_MNT_UNBINDABLE(mnt))
return ERR_PTR(-EINVAL);
if (!(flag & CL_COPY_MNT_NS_FILE) && is_mnt_ns_file(dentry))
return ERR_PTR(-EINVAL);
res = q = clone_mnt(mnt, dentry, flag);
@ -1397,7 +1409,13 @@ struct mount *copy_tree(struct mount *mnt, struct dentry *dentry,
continue;
for (s = r; s; s = next_mnt(s, r)) {
if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(s)) {
if (!(flag & CL_COPY_UNBINDABLE) &&
IS_MNT_UNBINDABLE(s)) {
s = skip_mnt_tree(s);
continue;
}
if (!(flag & CL_COPY_MNT_NS_FILE) &&
is_mnt_ns_file(s->mnt.mnt_root)) {
s = skip_mnt_tree(s);
continue;
}
@ -1733,7 +1751,7 @@ static int do_loopback(struct path *path, const char *old_name,
return err;
err = -EINVAL;
if (mnt_ns_loop(&old_path))
if (mnt_ns_loop(old_path.dentry))
goto out;
mp = lock_mount(path);
@ -1755,7 +1773,7 @@ static int do_loopback(struct path *path, const char *old_name,
goto out2;
if (recurse)
mnt = copy_tree(old, old_path.dentry, 0);
mnt = copy_tree(old, old_path.dentry, CL_COPY_MNT_NS_FILE);
else
mnt = clone_mnt(old, old_path.dentry, 0);
@ -2417,7 +2435,7 @@ static struct mnt_namespace *dup_mnt_ns(struct mnt_namespace *mnt_ns,
namespace_lock();
/* First pass: copy the tree topology */
copy_flags = CL_COPY_ALL | CL_EXPIRE;
copy_flags = CL_COPY_UNBINDABLE | CL_EXPIRE;
if (user_ns != mnt_ns->user_ns)
copy_flags |= CL_SHARED_TO_SLAVE | CL_UNPRIVILEGED;
new = copy_tree(old, old->mnt.mnt_root, copy_flags);
@ -2452,6 +2470,10 @@ static struct mnt_namespace *dup_mnt_ns(struct mnt_namespace *mnt_ns,
}
p = next_mnt(p, old);
q = next_mnt(q, new);
if (!q)
break;
while (p->mnt.mnt_root != q->mnt.mnt_root)
p = next_mnt(p, old);
}
namespace_unlock();

5
fs/pnode.h

@ -19,11 +19,14 @@
#define CL_EXPIRE 0x01
#define CL_SLAVE 0x02
#define CL_COPY_ALL 0x04
#define CL_COPY_UNBINDABLE 0x04
#define CL_MAKE_SHARED 0x08
#define CL_PRIVATE 0x10
#define CL_SHARED_TO_SLAVE 0x20
#define CL_UNPRIVILEGED 0x40
#define CL_COPY_MNT_NS_FILE 0x80
#define CL_COPY_ALL (CL_COPY_UNBINDABLE | CL_COPY_MNT_NS_FILE)
static inline void set_mnt_shared(struct mount *mnt)
{

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