[PATCH] ksmbd: fix memory leaks and NULL deref in smb2_lock()

[Werner Kasselman]

smb2_lock() has three error handling issues after list_del() detaches
smb_lock from lock_list at no_check_cl:

1) If vfs_lock_file() returns an unexpected error in the non-UNLOCK
   path, goto out leaks smb_lock and its flock because the out:
   handler only iterates lock_list and rollback_list, neither of
   which contains the detached smb_lock.

2) If vfs_lock_file() returns -ENOENT in the UNLOCK path, goto out
   leaks smb_lock and flock for the same reason.  The error code
   returned to the dispatcher is also stale.

3) In the rollback path, smb_flock_init() can return NULL on
   allocation failure.  The result is dereferenced unconditionally,
   causing a kernel NULL pointer dereference.  Add a NULL check to
   prevent the crash and clean up the bookkeeping; the VFS lock
   itself cannot be rolled back without the allocation and will be
   released at file or connection teardown.

Fix by freeing smb_lock and flock before goto out in cases 1 and 2,
propagating the correct error code, and adding a NULL check for the
rollback allocation in case 3.

Found via call-graph analysis using sqry.

Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Werner Kasselman <werner@xxxxxxxxxxx>
---
 fs/smb/server/smb2pdu.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
index 9f7ff7491e9a..36e281f5924a 100644
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -7583,6 +7583,9 @@ int smb2_lock(struct ksmbd_work *work)
 				ksmbd_debug(SMB, "File unlocked\n");
 			} else if (rc == -ENOENT) {
 				rsp->hdr.Status = STATUS_NOT_LOCKED;
+				locks_free_lock(flock);
+				kfree(smb_lock);
+				err = -ENOENT;
 				goto out;
 			}
 			locks_free_lock(flock);
@@ -7655,6 +7658,9 @@ int smb2_lock(struct ksmbd_work *work)
 				spin_unlock(&work->conn->llist_lock);
 				ksmbd_debug(SMB, "successful in taking lock\n");
 			} else {
+				locks_free_lock(flock);
+				kfree(smb_lock);
+				err = rc;
 				goto out;
 			}
 		}
@@ -7685,6 +7691,19 @@ int smb2_lock(struct ksmbd_work *work)
 		struct file_lock *rlock = NULL;
 
 		rlock = smb_flock_init(filp);
+		if (!rlock) {
+			pr_err("rollback unlock alloc failed\n");
+			list_del(&smb_lock->llist);
+			spin_lock(&work->conn->llist_lock);
+			if (!list_empty(&smb_lock->flist))
+				list_del(&smb_lock->flist);
+			list_del(&smb_lock->clist);
+			spin_unlock(&work->conn->llist_lock);
+
+			locks_free_lock(smb_lock->fl);
+			kfree(smb_lock);
+			continue;
+		}
 		rlock->c.flc_type = F_UNLCK;
 		rlock->fl_start = smb_lock->start;
 		rlock->fl_end = smb_lock->end;
-- 
2.43.0