[kernel-hardening] [PATCHv2 2/4] slub: Fix/clean free_debug_processing return paths

[Laura Abbott <labbott@fedoraproject.org>]

Since 19c7ff9ecd89 ("slub: Take node lock during object free checks")
check_object has been incorrectly returning success as it follows
the out label which just returns the node. Thanks to refactoring,
the out and fail paths are now basically the same. Combine the two
into one and just use a single label.

Credit to Mathias Krause for the original work which inspired this series

Signed-off-by: Laura Abbott <labbott@fedoraproject.org>
---
If there is interest, I can split this off as a separate patch for stable
---
 mm/slub.c | 21 ++++++++++-----------
 1 file changed, 10 insertions(+), 11 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 2d5a774..189c330 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1077,24 +1077,25 @@ static noinline int free_debug_processing(
 	void *object = head;
 	int cnt = 0;
 	unsigned long uninitialized_var(flags);
+	int ret = 0;
 
 	spin_lock_irqsave(&n->list_lock, flags);
 	slab_lock(page);
 
 	if (!check_slab(s, page))
-		goto fail;
+		goto out;
 
 next_object:
 	cnt++;
 
 	if (!check_valid_pointer(s, page, object)) {
 		slab_err(s, page, "Invalid object pointer 0x%p", object);
-		goto fail;
+		goto out;
 	}
 
 	if (on_freelist(s, page, object)) {
 		object_err(s, page, object, "Object already free");
-		goto fail;
+		goto out;
 	}
 
 	if (!check_object(s, page, object, SLUB_RED_ACTIVE))
@@ -1111,7 +1112,7 @@ next_object:
 		} else
 			object_err(s, page, object,
 					"page slab pointer corrupt.");
-		goto fail;
+		goto out;
 	}
 
 	if (s->flags & SLAB_STORE_USER)
@@ -1125,6 +1126,8 @@ next_object:
 		object = get_freepointer(s, object);
 		goto next_object;
 	}
+	ret = 1;
+
 out:
 	if (cnt != bulk_cnt)
 		slab_err(s, page, "Bulk freelist count(%d) invalid(%d)\n",
@@ -1132,13 +1135,9 @@ out:
 
 	slab_unlock(page);
 	spin_unlock_irqrestore(&n->list_lock, flags);
-	return 1;
-
-fail:
-	slab_unlock(page);
-	spin_unlock_irqrestore(&n->list_lock, flags);
-	slab_fix(s, "Object at 0x%p not freed", object);
-	return 0;
+	if (!ret)
+		slab_fix(s, "Object at 0x%p not freed", object);
+	return ret;
 }
 
 static int __init setup_slub_debug(char *str)
-- 
2.5.0