lkml.org 
[lkml]   [2020]   [Apr]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v2] mm/slub: Fix incorrect interpretation 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 like the
following to appear with the system in panic afterwards.

[ 38.579769] =============================================================================
[ 38.580845] BUG dentry(666:pmcd.service) (Tainted: G B): Freepointer corrupt
[ 38.581948] -----------------------------------------------------------------------------

To fix it, use the check "s->offset == s->inuse" in the new helper
function freeptr_after_object() instead. Also add another helper function
get_info_end() to return the end of info block (inuse + free pointer
if not overlapping with object).

Fixes: 3202fa62fb43 ("slub: relocate freelist pointer to middle of object")
Signed-off-by: Waiman Long <longman@redhat.com>
---
mm/slub.c | 37 ++++++++++++++++++++++---------------
1 file changed, 22 insertions(+), 15 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 0e736d66bb42..68f1b4b1c309 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -551,15 +551,29 @@ static void print_section(char *level, char *text, u8 *addr,
metadata_access_disable();
}

+static inline bool freeptr_after_object(struct kmem_cache *s)
+{
+ return s->offset == s->inuse;
+}
+
+/*
+ * Return offset of the end of info block which is inuse + free pointer if
+ * not overlapping with object.
+ */
+static inline unsigned int get_info_end(struct kmem_cache *s)
+{
+ if (freeptr_after_object(s))
+ return s->inuse + sizeof(void *);
+ else
+ return s->inuse;
+}
+
static struct track *get_track(struct kmem_cache *s, void *object,
enum track_item alloc)
{
struct track *p;

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

return p + alloc;
}
@@ -693,10 +707,7 @@ 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 = get_info_end(s);

if (s->flags & SLAB_STORE_USER)
off += 2 * sizeof(struct track);
@@ -790,7 +801,7 @@ 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)
@@ -824,11 +835,7 @@ static int check_bytes_and_report(struct kmem_cache *s, struct page *page,

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)
- /* Freepointer is placed after the object. */
- off += sizeof(void *);
+ unsigned long off = get_info_end(s); /* The end of info */

if (s->flags & SLAB_STORE_USER)
/* We also have user information there */
@@ -915,7 +922,7 @@ 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 (!freeptr_after_object(s) && val == SLUB_RED_ACTIVE)
/*
* Object and freepointer overlap. Cannot check
* freepointer while object is allocated.
--
2.18.1
\
 
 \ /
  Last update: 2020-04-27 16:09    [W:0.072 / U:0.796 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site