[PATCH 01/24] pidns: Remove races by stopping the caching of proc_mnt

[ebiederm@xmission.com (Eric W. Biederman)]

Having proc reference the pid_namespace and the pid_namespace
reference proc is a serious reference counting problem, which has
resulted in both leaks and use after free problems.  Mount already
knows how to go from a pid_namespace to a mount of proc, so we don't
need to cache the proc mount.

To do this I introduce get_proc_mnt and replace pid_ns->proc_mnt users
with it. Additionally I remove pid_ns_(prepare|release)_proc as they
are now unneeded.

This is slightly less efficient but it is much easier to avoid the
races.  If efficiency winds up being a problem we can revisit our data
structures.

Reported-by: Louis Rilling <Louis.Rilling@kerlabs.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
---
 arch/um/drivers/mconsole_kern.c |    4 +++-
 fs/hppfs/hppfs.c                |    2 +-
 fs/proc/base.c                  |   13 +++++++------
 fs/proc/root.c                  |   15 ++-------------
 include/linux/pid_namespace.h   |    3 ---
 include/linux/proc_fs.h         |   13 +------------
 kernel/fork.c                   |    6 ------
 kernel/sysctl_binary.c          |    3 ++-
 8 files changed, 16 insertions(+), 43 deletions(-)

diff --git a/arch/um/drivers/mconsole_kern.c b/arch/um/drivers/mconsole_kern.c
index de317d0..e89f72c 100644
--- a/arch/um/drivers/mconsole_kern.c
+++ b/arch/um/drivers/mconsole_kern.c
@@ -125,7 +125,7 @@ void mconsole_log(struct mc_request *req)
 void mconsole_proc(struct mc_request *req)
 {
 	struct nameidata nd;
-	struct vfsmount *mnt = current->nsproxy->pid_ns->proc_mnt;
+	struct vfsmount *mnt;
 	struct file *file;
 	int n, err;
 	char *ptr = req->request.data, *buf;
@@ -134,7 +134,9 @@ void mconsole_proc(struct mc_request *req)
 	ptr += strlen("proc");
 	ptr = skip_spaces(ptr);
 
+	mnt = get_proc_mnt(task_active_pid_ns(current));
 	err = vfs_path_lookup(mnt->mnt_root, mnt, ptr, LOOKUP_FOLLOW, &nd);
+	mntput(mnt);
 	if (err) {
 		mconsole_reply(req, "Failed to look up file", 1, 0);
 		goto out;
diff --git a/fs/hppfs/hppfs.c b/fs/hppfs/hppfs.c
index 826c3f9..79e61ab 100644
--- a/fs/hppfs/hppfs.c
+++ b/fs/hppfs/hppfs.c
@@ -718,7 +718,7 @@ static int hppfs_fill_super(struct super_block *sb, void *d, int silent)
 	struct vfsmount *proc_mnt;
 	int err = -ENOENT;
 
-	proc_mnt = mntget(current->nsproxy->pid_ns->proc_mnt);
+	proc_mnt = get_proc_mnt(task_active_pid_ns(current));
 	if (IS_ERR(proc_mnt))
 		goto out;
 
diff --git a/fs/proc/base.c b/fs/proc/base.c
index acb7ef8..93a3ee9 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2735,6 +2735,7 @@ void proc_flush_task(struct task_struct *task)
 {
 	int i;
 	struct pid *pid, *tgid;
+	struct vfsmount *mnt;
 	struct upid *upid;
 
 	pid = task_pid(task);
@@ -2742,13 +2743,13 @@ void proc_flush_task(struct task_struct *task)
 
 	for (i = 0; i <= pid->level; i++) {
 		upid = &pid->numbers[i];
-		proc_flush_task_mnt(upid->ns->proc_mnt, upid->nr,
-					tgid->numbers[i].nr);
-	}
+		mnt = get_proc_mnt(upid->ns);
+		if (IS_ERR(mnt))
+			continue;
 
-	upid = &pid->numbers[pid->level];
-	if (upid->nr == 1)
-		pid_ns_release_proc(upid->ns);
+		proc_flush_task_mnt(mnt, upid->nr, tgid->numbers[i].nr);
+		mntput(mnt);
+	}
 }
 
 static struct dentry *proc_pid_instantiate(struct inode *dir,
diff --git a/fs/proc/root.c b/fs/proc/root.c
index 4258384..c042015 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -79,7 +79,6 @@ static int proc_get_sb(struct file_system_type *fs_type,
 		}
 
 		sb->s_flags |= MS_ACTIVE;
-		ns->proc_mnt = mnt;
 	}
 
 	simple_set_mnt(mnt, sb);
@@ -204,18 +203,8 @@ struct proc_dir_entry proc_root = {
 	.parent		= &proc_root,
 };
 
-int pid_ns_prepare_proc(struct pid_namespace *ns)
+struct vfsmount *get_proc_mnt(struct pid_namespace *ns)
 {
-	struct vfsmount *mnt;
-
-	mnt = kern_mount_data(&proc_fs_type, ns);
-	if (IS_ERR(mnt))
-		return PTR_ERR(mnt);
-
-	return 0;
+	return kern_mount_data(&proc_fs_type, ns);
 }
 
-void pid_ns_release_proc(struct pid_namespace *ns)
-{
-	mntput(ns->proc_mnt);
-}
diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
index 38d1032..3feb917 100644
--- a/include/linux/pid_namespace.h
+++ b/include/linux/pid_namespace.h
@@ -24,9 +24,6 @@ struct pid_namespace {
 	struct kmem_cache *pid_cachep;
 	unsigned int level;
 	struct pid_namespace *parent;
-#ifdef CONFIG_PROC_FS
-	struct vfsmount *proc_mnt;
-#endif
 #ifdef CONFIG_BSD_PROCESS_ACCT
 	struct bsd_acct_struct *bacct;
 #endif
diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index 379eaed..6b7a416 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -103,6 +103,7 @@ struct vmcore {
 #ifdef CONFIG_PROC_FS
 
 extern void proc_root_init(void);
+struct vfsmount *get_proc_mnt(struct pid_namespace *ns);
 
 void proc_flush_task(struct task_struct *task);
 
@@ -116,9 +117,6 @@ extern void remove_proc_entry(const char *name, struct proc_dir_entry *parent);
 
 struct pid_namespace;
 
-extern int pid_ns_prepare_proc(struct pid_namespace *ns);
-extern void pid_ns_release_proc(struct pid_namespace *ns);
-
 /*
  * proc_tty.c
  */
@@ -217,15 +215,6 @@ struct tty_driver;
 static inline void proc_tty_register_driver(struct tty_driver *driver) {};
 static inline void proc_tty_unregister_driver(struct tty_driver *driver) {};
 
-static inline int pid_ns_prepare_proc(struct pid_namespace *ns)
-{
-	return 0;
-}
-
-static inline void pid_ns_release_proc(struct pid_namespace *ns)
-{
-}
-
 static inline void set_mm_exe_file(struct mm_struct *mm,
 				   struct file *new_exe_file)
 {}
diff --git a/kernel/fork.c b/kernel/fork.c
index b6cce14..b063a9c 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1154,12 +1154,6 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 		pid = alloc_pid(p->nsproxy->pid_ns);
 		if (!pid)
 			goto bad_fork_cleanup_io;
-
-		if (clone_flags & CLONE_NEWPID) {
-			retval = pid_ns_prepare_proc(p->nsproxy->pid_ns);
-			if (retval < 0)
-				goto bad_fork_free_pid;
-		}
 	}
 
 	p->pid = pid_nr(pid);
diff --git a/kernel/sysctl_binary.c b/kernel/sysctl_binary.c
index 1357c57..68f302a 100644
--- a/kernel/sysctl_binary.c
+++ b/kernel/sysctl_binary.c
@@ -1350,8 +1350,9 @@ static ssize_t binary_sysctl(const int *name, int nlen,
 		goto out_putname;
 	}
 
-	mnt = current->nsproxy->pid_ns->proc_mnt;
+	mnt = get_proc_mnt(task_active_pid_ns(current));
 	result = vfs_path_lookup(mnt->mnt_root, mnt, pathname, 0, &nd);
+	mntput(mnt);
 	if (result)
 		goto out_putname;
 
-- 
1.6.5.2.143.g8cc62