ceph: fix possible NULL pointer dereference for req->r_session

The request will be inserted into the ci->i_unsafe_dirops before
assigning the req->r_session, so it's possible that we will hit
NULL pointer dereference bug here.

Cc: [email protected]
URL: https://tracker.ceph.com/issues/55327
Signed-off-by: Xiubo Li <[email protected]>
Reviewed-by: Jeff Layton <[email protected]>
Tested-by: Aaron Tomlin <[email protected]>
Signed-off-by: Ilya Dryomov <[email protected]>

Author: lxbsz

fs/ceph/caps.c

@@ -2274,6 +2274,8 @@ static int unsafe_request_wait(struct inode *inode)
 			list_for_each_entry(req, &ci->i_unsafe_dirops,
 					    r_unsafe_dir_item) {
 				s = req->r_session;
+				if (!s)
+					continue;
 				if (unlikely(s->s_mds >= max_sessions)) {
 					spin_unlock(&ci->i_unsafe_lock);
 					for (i = 0; i < max_sessions; i++) {
@@ -2294,6 +2296,8 @@ static int unsafe_request_wait(struct inode *inode)
 			list_for_each_entry(req, &ci->i_unsafe_iops,
 					    r_unsafe_target_item) {
 				s = req->r_session;
+				if (!s)
+					continue;
 				if (unlikely(s->s_mds >= max_sessions)) {
 					spin_unlock(&ci->i_unsafe_lock);
 					for (i = 0; i < max_sessions; i++) {