Re: [PATCH v3] cred: Propagate security_prepare_creds() error code

Hi Eric,

On 6/9/22 6:18 PM, Eric Biggers wrote:

On Wed, Jun 08, 2022 at 10:09:42AM -0500, Frederick Lawler wrote:

quoted

diff --git a/fs/aio.c b/fs/aio.c
index 3c249b938632..5abbe88c3ca7 100644
--- a/fs/aio.c
+++ b/fs/aio.c

@@ -1620,6 +1620,8 @@ static void aio_fsync_work(struct work_struct *work)
  static int aio_fsync(struct fsync_iocb *req, const struct iocb *iocb,
  		     bool datasync)
  {
+	int err;
+
  	if (unlikely(iocb->aio_buf || iocb->aio_offset || iocb->aio_nbytes ||
  			iocb->aio_rw_flags))
  		return -EINVAL;

@@ -1628,8 +1630,11 @@ static int aio_fsync(struct fsync_iocb *req, const struct iocb *iocb,
  		return -EINVAL;
  
  	req->creds = prepare_creds();
-	if (!req->creds)
-		return -ENOMEM;
+	if (IS_ERR(req->creds)) {
+		err = PTR_ERR(req->creds);
+		req->creds = NULL;
+		return err;
+	}

This part is a little ugly.  How about doing:

	creds = prepare_creds();
	if (IS_ERR(creds))
		return PTR_ERR(creds);
	req->creds = creds;

I can do that, and same for below.

quoted

diff --git a/fs/exec.c b/fs/exec.c
index 0989fb8472a1..02624783e40e 100644
--- a/fs/exec.c
+++ b/fs/exec.c

@@ -1468,15 +1468,19 @@ EXPORT_SYMBOL(finalize_exec);
   */
  static int prepare_bprm_creds(struct linux_binprm *bprm)
  {
+	int err = -ERESTARTNOINTR;
  	if (mutex_lock_interruptible(&current->signal->cred_guard_mutex))
-		return -ERESTARTNOINTR;
+		return err;
  
  	bprm->cred = prepare_exec_creds();
-	if (likely(bprm->cred))
-		return 0;
+	if (IS_ERR(bprm->cred)) {
+		err = PTR_ERR(bprm->cred);
+		bprm->cred = NULL;
+		mutex_unlock(&current->signal->cred_guard_mutex);
+		return err;
+	}
  
-	mutex_unlock(&current->signal->cred_guard_mutex);
-	return -ENOMEM;
+	return 0;
  }

Similarly:

static int prepare_bprm_creds(struct linux_binprm *bprm)
{
	struct cred *cred;

	if (mutex_lock_interruptible(&current->signal->cred_guard_mutex))
		return -ERESTARTNOINTR;

	cred = prepare_exec_creds();
	if (IS_ERR(cred)) {
		mutex_unlock(&current->signal->cred_guard_mutex);
		return PTR_ERR(cred);
	}
	bprm->cred = cred;
	return 0;
}

quoted

diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
index eec72ca962e2..6cf75aa83b6c 100644
--- a/kernel/nsproxy.c
+++ b/kernel/nsproxy.c

@@ -311,6 +311,7 @@ static void put_nsset(struct nsset *nsset)
  
  static int prepare_nsset(unsigned flags, struct nsset *nsset)
  {
+	int err = -ENOMEM;
  	struct task_struct *me = current;
  
  	nsset->nsproxy = create_new_namespaces(0, me, current_user_ns(), me->fs);

@@ -324,6 +325,12 @@ static int prepare_nsset(unsigned flags, struct nsset *nsset)
  	if (!nsset->cred)
  		goto out;
  
+	if (IS_ERR(nsset->cred)) {
+		err = PTR_ERR(nsset->cred);
+		nsset->cred = NULL;
+		goto out;
+	}

Why is the NULL check above being kept?

In the branch prior:

	if (flags & CLONE_NEWUSER) {
		nsset->cred = prepare_creds();
	else
		nsset->cred = current_cred();

I don't see cases where others are checking for null after 
current_cred(), therefore I can remove that check.

Also, drivers/crypto/ccp/sev-dev.c needs to be updated.

Nice catch! I clearly missed addition after the merge window.

- Eric