On 08/07/10 21:39 -0700, Eric W. Biederman wrote:
>
> Currently it is possible to put proc_mnt before we have flushed the
> last process that will use the proc_mnt to flush it's proc entries.
>
> This race is fixed by not flushing proc entries for dead pid
> namespaces, and calling pid_ns_release_proc unconditionally from
> zap_pid_ns_processes after the pid namespace has been declared dead.
One comment below.
>
> To ensure we don't unnecessarily leak any dcache entries with skipped
> flushes pid_ns_release_proc flushes the entire proc_mnt when it is
> called.
>
> Signed-off-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
> ---
> fs/proc/base.c | 9 +++++----
> fs/proc/root.c | 3 +++
> kernel/pid_namespace.c | 1 +
> 3 files changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index acb7ef8..e9d84e1 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -2742,13 +2742,14 @@ void proc_flush_task(struct task_struct *task)
>
> for (i = 0; i <= pid->level; i++) {
> upid = &pid->numbers[i];
> +
> + /* Don't bother flushing dead pid namespaces */
> + if (test_bit(PIDNS_DEAD, &upid->ns->flags))
> + continue;
> +
IMHO, nothing prevents zap_pid_ns_processes() from setting PIDNS_DEAD and
calling pid_ns_release_proc() right now. zap_pid_ns_processes() does not wait
for EXIT_DEAD (self-reaping) children to be released.
Thanks,
Louis
> proc_flush_task_mnt(upid->ns->proc_mnt, upid->nr,
> tgid->numbers[i].nr);
> }
> -
> - upid = &pid->numbers[pid->level];
> - if (upid->nr == 1)
> - pid_ns_release_proc(upid->ns);
> }
>
> static struct dentry *proc_pid_instantiate(struct inode *dir,
> diff --git a/fs/proc/root.c b/fs/proc/root.c
> index cfdf032..2298fdd 100644
> --- a/fs/proc/root.c
> +++ b/fs/proc/root.c
> @@ -209,5 +209,8 @@ int pid_ns_prepare_proc(struct pid_namespace *ns)
>
> void pid_ns_release_proc(struct pid_namespace *ns)
> {
> + /* Flush any cached proc dentries for this pid namespace */
> + shrink_dcache_parent(ns->proc_mnt->mnt_root);
> +
> mntput(ns->proc_mnt);
> }
> diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
> index 92032d1..43dec5d 100644
> --- a/kernel/pid_namespace.c
> +++ b/kernel/pid_namespace.c
> @@ -189,6 +189,7 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
> rc = sys_wait4(-1, NULL, __WALL, NULL);
> } while (rc != -ECHILD);
>
> + pid_ns_release_proc(pid_ns);
> acct_exit_ns(pid_ns);
> return;
> }
> --
> 1.6.5.2.143.g8cc62
>
> --
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--
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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