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Message-ID: <20100711141406.GD18586@hawkmoon.kerlabs.com>
Date: Sun, 11 Jul 2010 16:14:07 +0200
From: Louis Rilling <Louis.Rilling@...labs.com>
To: "Eric W. Biederman" <ebiederm@...ssion.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Linux Containers <containers@...ts.osdl.org>,
Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
linux-kernel@...r.kernel.org, Pavel Emelyanov <xemul@...nvz.org>,
Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH 01/24] pidns: Remove races by stopping the caching of
proc_mnt
On 09/07/10 8:58 -0700, Eric W. Biederman wrote:
>
> 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.
IIUC, the difference between this solution and the first one I proposed is that
instead of pinning proc_mnt with mntget() at copy_process()-time, proc_mnt is
looked for and, if possible, mntget() at release_task()-time.
Could you elaborate on the trade-off, that is accessing proc_mnt at
copy_process()-time vs looking up proc_mnt at release_task()-time?
Thanks,
Louis
>
> Reported-by: Louis Rilling <Louis.Rilling@...labs.com>
> Signed-off-by: Eric W. Biederman <ebiederm@...ssion.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
>
--
Dr Louis Rilling Kerlabs
Skype: louis.rilling Batiment Germanium
Phone: (+33|0) 6 80 89 08 23 80 avenue des Buttes de Coesmes
http://www.kerlabs.com/ 35700 Rennes
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