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@xxxxxxxxxxxx>
---
fs/namespace.c | 46 ++++++++++++++++++++++++++++++++++------------
fs/pnode.h | 5 ++++-
2 files changed, 38 insertions(+), 13 deletions(-)
diff --git a/fs/namespace.c b/fs/namespace.c
index 7e16a73..64627f8 100644
--- a/fs/namespace.c
+++ b/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();
diff --git a/fs/pnode.h b/fs/pnode.h
index b091445..59e7eda 100644
--- a/fs/pnode.h
+++ b/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)
{
--
1.7.5.4
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