mm, slub: fix two bugs in slab_debug_trace_open()

Patch series "Fixups for slub".

This series contains various bug fixes for slub.  We fix memoryleak,
use-afer-free, NULL pointer dereferencing and so on in slub.  More
details can be found in the respective changelogs.

This patch (of 5):

It's possible that __seq_open_private() will return NULL.  So we should
check it before using lest dereferencing NULL pointer.  And in error
paths, we forgot to release private buffer via seq_release_private().
Memory will leak in these paths.

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Fixes: 64dd684 ("mm: slub: move sysfs slab alloc/free interfaces to debugfs")
Signed-off-by: Miaohe Lin <[email protected]>
Reviewed-by: Vlastimil Babka <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Faiyaz Mohammed <[email protected]>
Cc: Andrey Konovalov <[email protected]>
Cc: Andrey Ryabinin <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Bharata B Rao <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/slub.c

@@ -6108,9 +6108,14 @@ static int slab_debug_trace_open(struct inode *inode, struct file *filep)
 	struct kmem_cache *s = file_inode(filep)->i_private;
 	unsigned long *obj_map;
 
+	if (!t)
+		return -ENOMEM;
+
 	obj_map = bitmap_alloc(oo_objects(s->oo), GFP_KERNEL);
-	if (!obj_map)
+	if (!obj_map) {
+		seq_release_private(inode, filep);
 		return -ENOMEM;
+	}
 
 	if (strcmp(filep->f_path.dentry->d_name.name, "alloc_traces") == 0)
 		alloc = TRACK_ALLOC;
@@ -6119,6 +6124,7 @@ static int slab_debug_trace_open(struct inode *inode, struct file *filep)
 
 	if (!alloc_loc_track(t, PAGE_SIZE / sizeof(struct location), GFP_KERNEL)) {
 		bitmap_free(obj_map);
+		seq_release_private(inode, filep);
 		return -ENOMEM;
 	}