xfs: transfer recovered intent item ownership in ->iop_recover

Now that we pass the xfs_defer_pending object into the intent item
recovery functions, we know exactly when ownership of the sole refcount
passes from the recovery context to the intent done item.  At that
point, we need to null out dfp_intent so that the recovery mechanism
won't release it.  This should fix the UAF problem reported by Long Li.

Note that we still want to recreate the full deferred work state.  That
will be addressed in the next patches.

Fixes: 2e76f188 ("xfs: cancel intents immediately if process_intents fails")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/xfs/libxfs/xfs_log_recover.h

@@ -155,5 +155,7 @@ xlog_recover_resv(const struct xfs_trans_res *r)
 
 void xlog_recover_intent_item(struct xlog *log, struct xfs_log_item *lip,
 		xfs_lsn_t lsn, unsigned int dfp_type);
+void xlog_recover_transfer_intent(struct xfs_trans *tp,
+		struct xfs_defer_pending *dfp);
 
 #endif	/* __XFS_LOG_RECOVER_H__ */

fs/xfs/xfs_attr_item.c

@@ -632,6 +632,7 @@ xfs_attri_item_recover(
 
 	args->trans = tp;
 	done_item = xfs_trans_get_attrd(tp, attrip);
+	xlog_recover_transfer_intent(tp, dfp);
 
 	xfs_ilock(ip, XFS_ILOCK_EXCL);
 	xfs_trans_ijoin(tp, ip, 0);

fs/xfs/xfs_bmap_item.c

@@ -524,6 +524,8 @@ xfs_bui_item_recover(
 		goto err_rele;
 
 	budp = xfs_trans_get_bud(tp, buip);
+	xlog_recover_transfer_intent(tp, dfp);
+
 	xfs_ilock(ip, XFS_ILOCK_EXCL);
 	xfs_trans_ijoin(tp, ip, 0);
 

fs/xfs/xfs_extfree_item.c

@@ -689,7 +689,9 @@ xfs_efi_item_recover(
 	error = xfs_trans_alloc(mp, &resv, 0, 0, 0, &tp);
 	if (error)
 		return error;
+
 	efdp = xfs_trans_get_efd(tp, efip, efip->efi_format.efi_nextents);
+	xlog_recover_transfer_intent(tp, dfp);
 
 	for (i = 0; i < efip->efi_format.efi_nextents; i++) {
 		struct xfs_extent_free_item	fake = {

fs/xfs/xfs_log_recover.c

@@ -2590,13 +2590,6 @@ xlog_recover_process_intents(
 			break;
 		}
 
-		/*
-		 * XXX: @lip could have been freed, so detach the log item from
-		 * the pending item before freeing the pending item.  This does
-		 * not fix the existing UAF bug that occurs if ->iop_recover
-		 * fails after creating the intent done item.
-		 */
-		dfp->dfp_intent = NULL;
 		xfs_defer_cancel_recovery(log->l_mp, dfp);
 	}
 	if (error)
@@ -2630,6 +2623,18 @@ xlog_recover_cancel_intents(
 	}
 }
 
+/*
+ * Transfer ownership of the recovered log intent item to the recovery
+ * transaction.
+ */
+void
+xlog_recover_transfer_intent(
+	struct xfs_trans		*tp,
+	struct xfs_defer_pending	*dfp)
+{
+	dfp->dfp_intent = NULL;
+}
+
 /*
  * This routine performs a transaction to null out a bad inode pointer
  * in an agi unlinked inode hash bucket.

fs/xfs/xfs_refcount_item.c

@@ -523,6 +523,7 @@ xfs_cui_item_recover(
 		return error;
 
 	cudp = xfs_trans_get_cud(tp, cuip);
+	xlog_recover_transfer_intent(tp, dfp);
 
 	for (i = 0; i < cuip->cui_format.cui_nextents; i++) {
 		struct xfs_refcount_intent	fake = { };

fs/xfs/xfs_rmap_item.c

@@ -537,7 +537,9 @@ xfs_rui_item_recover(
 			XFS_TRANS_RESERVE, &tp);
 	if (error)
 		return error;
+
 	rudp = xfs_trans_get_rud(tp, ruip);
+	xlog_recover_transfer_intent(tp, dfp);
 
 	for (i = 0; i < ruip->rui_format.rui_nextents; i++) {
 		struct xfs_rmap_intent	fake = { };