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Subject[PATCH] mm/slub: Fix incorrect checkings of s->offset
Date
In a couple of places in the slub memory allocator, the code uses
"s->offset" as a check to see if the free pointer is put right after the
object. That check is no longer true with commit 3202fa62fb43 ("slub:
relocate freelist pointer to middle of object").

As a result, echoing "1" into the validate sysfs file, e.g. of dentry,
may cause a bunch of "Freepointer corrupt" error reports to appear with
the system in panic afterwards.

To fix it, use the check "s->offset == s->inuse" instead.

Fixes: 3202fa62fb43 ("slub: relocate freelist pointer to middle of object")
Signed-off-by: Waiman Long <longman@redhat.com>
---
mm/slub.c | 18 +++++++-----------
1 file changed, 7 insertions(+), 11 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 0e736d66bb42..99952d01e7e0 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -556,10 +556,8 @@ static struct track *get_track(struct kmem_cache *s, void *object,
{
struct track *p;

- if (s->offset)
- p = object + s->offset + sizeof(void *);
- else
- p = object + s->inuse;
+ p = object + s->inuse +
+ ((s->offset == s->inuse) ? sizeof(void *) : 0);

return p + alloc;
}
@@ -693,10 +691,8 @@ static void print_trailer(struct kmem_cache *s, struct page *page, u8 *p)
print_section(KERN_ERR, "Redzone ", p + s->object_size,
s->inuse - s->object_size);

- if (s->offset)
- off = s->offset + sizeof(void *);
- else
- off = s->inuse;
+ off = s->inuse +
+ ((s->offset == s->inuse) ? sizeof(void *) : 0);

if (s->flags & SLAB_STORE_USER)
off += 2 * sizeof(struct track);
@@ -790,7 +786,7 @@ static int check_bytes_and_report(struct kmem_cache *s, struct page *page,
* object address
* Bytes of the object to be managed.
* If the freepointer may overlay the object then the free
- * pointer is the first word of the object.
+ * pointer is at the middle of the object.
*
* Poisoning uses 0x6b (POISON_FREE) and the last byte is
* 0xa5 (POISON_END)
@@ -826,7 +822,7 @@ static int check_pad_bytes(struct kmem_cache *s, struct page *page, u8 *p)
{
unsigned long off = s->inuse; /* The end of info */

- if (s->offset)
+ if (s->offset == s->inuse)
/* Freepointer is placed after the object. */
off += sizeof(void *);

@@ -915,7 +911,7 @@ static int check_object(struct kmem_cache *s, struct page *page,
check_pad_bytes(s, page, p);
}

- if (!s->offset && val == SLUB_RED_ACTIVE)
+ if ((s->offset != s->inuse) && val == SLUB_RED_ACTIVE)
/*
* Object and freepointer overlap. Cannot check
* freepointer while object is allocated.
--
2.18.1
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