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From: Eric W. Biederman on 9 Jul 2010 12:00

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(a)kerlabs.com>
Signed-off-by: Eric W. Biederman <ebiederm(a)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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Prev: PCI: skip release and reallocation of io port resources
Next: [PATCH 2/2] Add trace point to mremap