[PATCH 1/2] dlm: fix user space lkb refcounting

[Alexander Aring <aahringo@redhat.com>]

This patch fixes to check on the right return value if it was the last
callback. The rv variable got overwritten by the return of
copy_result_to_user(). Fixing it by introducing a second variable for
the return value and don't let rv being overwritten.

Cc: stable@vger.kernel.org
Fixes: 61bed0baa4db ("fs: dlm: use a non-static queue for callbacks")
Reported-by: Valentin Vidić <vvidic@valentin-vidic.from.hr>
Closes: https://lore.kernel.org/gfs2/Ze4qSvzGJDt5yxC3@valentin-vidic.from.hr
Signed-off-by: Alexander Aring <aahringo@redhat.com>
---
 fs/dlm/user.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/fs/dlm/user.c b/fs/dlm/user.c
index 695e691b38b3..9f9b68448830 100644
--- a/fs/dlm/user.c
+++ b/fs/dlm/user.c
@@ -806,7 +806,7 @@ static ssize_t device_read(struct file *file, char __user *buf, size_t count,
 	struct dlm_lkb *lkb;
 	DECLARE_WAITQUEUE(wait, current);
 	struct dlm_callback *cb;
-	int rv, copy_lvb = 0;
+	int rv, ret, copy_lvb = 0;
 	int old_mode, new_mode;
 
 	if (count == sizeof(struct dlm_device_version)) {
@@ -906,9 +906,9 @@ static ssize_t device_read(struct file *file, char __user *buf, size_t count,
 		trace_dlm_ast(lkb->lkb_resource->res_ls, lkb);
 	}
 
-	rv = copy_result_to_user(lkb->lkb_ua,
-				 test_bit(DLM_PROC_FLAGS_COMPAT, &proc->flags),
-				 cb->flags, cb->mode, copy_lvb, buf, count);
+	ret = copy_result_to_user(lkb->lkb_ua,
+				  test_bit(DLM_PROC_FLAGS_COMPAT, &proc->flags),
+				  cb->flags, cb->mode, copy_lvb, buf, count);
 
 	kref_put(&cb->ref, dlm_release_callback);
 
@@ -916,7 +916,7 @@ static ssize_t device_read(struct file *file, char __user *buf, size_t count,
 	if (rv == DLM_DEQUEUE_CALLBACK_LAST)
 		dlm_put_lkb(lkb);
 
-	return rv;
+	return ret;
 }
 
 static __poll_t device_poll(struct file *file, poll_table *wait)
-- 
2.43.0