[PATCH] pidfs: check for valid pid namespace

[PATCH] pidfs: check for valid pid namespace

[Christian Brauner]

When we access a no-current task's pid namespace we need check that the
task hasn't been reaped in the meantime and it's pid namespace isn't
accessible anymore.

The user namespace is fine because it is only released when the last
reference to struct task_struct is put and exit_creds() is called.

Fixes: 5b08bd408534 ("pidfs: allow retrieval of namespace file descriptors")
CC: stable@vger.kernel.org # v6.11
Signed-off-by: Christian Brauner <brauner@kernel.org>
---
 fs/pidfs.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/pidfs.c b/fs/pidfs.c
index 7ffdc88dfb52..80675b6bf884 100644
--- a/fs/pidfs.c
+++ b/fs/pidfs.c
@@ -120,6 +120,7 @@ static long pidfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	struct nsproxy *nsp __free(put_nsproxy) = NULL;
 	struct pid *pid = pidfd_pid(file);
 	struct ns_common *ns_common = NULL;
+	struct pid_namespace *pid_ns;
 
 	if (arg)
 		return -EINVAL;
@@ -202,7 +203,9 @@ static long pidfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	case PIDFD_GET_PID_NAMESPACE:
 		if (IS_ENABLED(CONFIG_PID_NS)) {
 			rcu_read_lock();
-			ns_common = to_ns_common( get_pid_ns(task_active_pid_ns(task)));
+			pid_ns = task_active_pid_ns(task);
+			if (pid_ns)
+				ns_common = to_ns_common(get_pid_ns(pid_ns));
 			rcu_read_unlock();
 		}
 		break;
-- 
2.45.2

Re: [PATCH] pidfs: check for valid pid namespace

[Josef Bacik]

On Thu, Sep 26, 2024 at 06:51:46PM +0200, Christian Brauner wrote:
> When we access a no-current task's pid namespace we need check that the
> task hasn't been reaped in the meantime and it's pid namespace isn't
> accessible anymore.
> 
> The user namespace is fine because it is only released when the last
> reference to struct task_struct is put and exit_creds() is called.
> 
> Fixes: 5b08bd408534 ("pidfs: allow retrieval of namespace file descriptors")
> CC: stable@vger.kernel.org # v6.11
> Signed-off-by: Christian Brauner <brauner@kernel.org>

Reviewed-by: Josef Bacik <josef@toxicpanda.com>

Thanks,

Josef