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

    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


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