Commit cbfc35a4 authored by Waiman Long's avatar Waiman Long Committed by Linus Torvalds
Browse files

mm/slub: fix incorrect interpretation of s->offset 



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 3202fa62 ("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.

  =============================================================================
  BUG dentry(666:pmcd.service) (Tainted: G    B): Freepointer corrupt
  -----------------------------------------------------------------------------

To fix it, use the check "s->offset == s->inuse" in the new helper
function freeptr_outside_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: 3202fa62 ("slub: relocate freelist pointer to middle of object")
Signed-off-by: default avatarWaiman Long <longman@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: default avatarMatthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Acked-by: default avatarRafael Aquini <aquini@redhat.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Vitaly Nikolenko <vnik@duasynt.com>
Cc: Silvio Cesare <silvio.cesare@gmail.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Markus Elfring <Markus.Elfring@web.de>
Cc: Changbin Du <changbin.du@gmail.com>
Link: http://lkml.kernel.org/r/20200429135328.26976-1-longman@redhat.com


Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 50e36be1

mm/slub.c

+30 −15
Original line number Diff line number Diff line
@@ -551,15 +551,32 @@ static void print_section(char *level, char *text, u8 *addr, 
	metadata_access_disable();

}



/*

 * See comment in calculate_sizes().

 */

static inline bool freeptr_outside_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_outside_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;

}
@@ -686,10 +703,7 @@ 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);
@@ -782,7 +796,7 @@ 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)
@@ -816,11 +830,7 @@ 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 */
@@ -907,7 +917,7 @@ 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_outside_object(s) && val == SLUB_RED_ACTIVE)

		/*

		 * Object and freepointer overlap. Cannot check

		 * freepointer while object is allocated.
@@ -3587,6 +3597,11 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order) 
		 *

		 * This is the case if we do RCU, have a constructor or

		 * destructor or are poisoning the objects.

		 *

		 * The assumption that s->offset >= s->inuse means free

		 * pointer is outside of the object is used in the

		 * freeptr_outside_object() function. If that is no

		 * longer true, the function needs to be modified.

		 */

		s->offset = size;

		size += sizeof(void *);

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