[PATCH v2] mm: slub: fix the leak of alloc/free traces debugfs interface

[Faiyaz Mohammed]

Fix the leak of alloc/free traces debugfs interface, reported
by kmemleak like below,

unreferenced object 0xffff00091ae1b540 (size 64):
  comm "lsbug", pid 1607, jiffies 4294958291 (age 1476.340s)
  hex dump (first 32 bytes):
    02 00 00 00 00 00 00 00 6b 6b 6b 6b 6b 6b 6b 6b  ........kkkkkkkk
    6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
  backtrace:
    [<ffff8000106b06b8>] slab_post_alloc_hook+0xa0/0x418
    [<ffff8000106b5c7c>] kmem_cache_alloc_trace+0x1e4/0x378
    [<ffff8000106b5e40>] slab_debugfs_start+0x30/0x50
    slab_debugfs_start at mm/slub.c:5831
    [<ffff8000107b3dbc>] seq_read_iter+0x214/0xd50
    [<ffff8000107b4b84>] seq_read+0x28c/0x418
    [<ffff8000109560b4>] full_proxy_read+0xdc/0x148
    [<ffff800010738f24>] vfs_read+0x104/0x340
    [<ffff800010739ee0>] ksys_read+0xf8/0x1e0
    [<ffff80001073a03c>] __arm64_sys_read+0x74/0xa8

Fixes: 3589836402ca ("mm: slub: move sysfs slab alloc/free interfaces to debugfs")
Link: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/mm/slub.c?h=next-20210617&id=84a2bdb1b458fc968d6d9e07dab388dc679bd747
Signed-off-by: Faiyaz Mohammed <faiyazm@xxxxxxxxxxxxxx>
---
v2 changes:
	- Updated the comparison in slab_debugfs_next().

v1 changes:
	- https://lore.kernel.org/linux-mm/1624019875-611-1-git-send-email-faiyazm@xxxxxxxxxxxxxx/

 mm/slub.c | 20 ++++++--------------
 1 file changed, 6 insertions(+), 14 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index fcb0c50..971d61d 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -5785,31 +5785,23 @@ static int slab_debugfs_show(struct seq_file *seq, void *v)
 
 static void slab_debugfs_stop(struct seq_file *seq, void *v)
 {
-	kfree(v);
 }
 
 static void *slab_debugfs_next(struct seq_file *seq, void *v, loff_t *ppos)
 {
-	loff_t *spos = v;
 	struct loc_track *t = seq->private;
 
-	if (*ppos < t->count) {
-		*ppos = ++*spos;
-		return spos;
-	}
-	*ppos = ++*spos;
+	v = ppos;
+	++*ppos;
+	if (*ppos <= t->count)
+		return v;
+
 	return NULL;
 }
 
 static void *slab_debugfs_start(struct seq_file *seq, loff_t *ppos)
 {
-	loff_t *spos = kmalloc(sizeof(loff_t), GFP_KERNEL);
-
-	if (!spos)
-		return NULL;
-
-	*spos = *ppos;
-	return spos;
+	return ppos;
 }
 
 static const struct seq_operations slab_debugfs_sops = {
-- 
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
member of the Code Aurora Forum, hosted by The Linux Foundation