Commit 89b83f28 authored by Kees Cook's avatar Kees Cook Committed by Linus Torvalds

slub: avoid redzone when choosing freepointer location

Marco Elver reported system crashes when booting with "slub_debug=Z".

The freepointer location (s->offset) was not taking into account that
the "inuse" size that includes the redzone area should not be used by
the freelist pointer.  Change the calculation to save the area of the
object that an inline freepointer may be written into.

Fixes: 3202fa62 ("slub: relocate freelist pointer to middle of object")
Reported-by: default avatarMarco Elver <>
Signed-off-by: default avatarKees Cook <>
Signed-off-by: default avatarAndrew Morton <>
Tested-by: default avatarMarco Elver <>
Cc: Christoph Lameter <>
Cc: Pekka Enberg <>
Cc: David Rientjes <>
Cc: Joonsoo Kim <>
Link: default avatarLinus Torvalds <>
parent 1eb64c07
......@@ -3533,6 +3533,7 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
slab_flags_t flags = s->flags;
unsigned int size = s->object_size;
unsigned int freepointer_area;
unsigned int order;
......@@ -3541,6 +3542,13 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
* the possible location of the free pointer.
size = ALIGN(size, sizeof(void *));
* This is the area of the object where a freepointer can be
* safely written. If redzoning adds more to the inuse size, we
* can't use that portion for writing the freepointer, so
* s->offset must be limited within this for the general case.
freepointer_area = size;
......@@ -3582,13 +3590,13 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
s->offset = size;
size += sizeof(void *);
} else if (size > sizeof(void *)) {
} else if (freepointer_area > sizeof(void *)) {
* Store freelist pointer near middle of object to keep
* it away from the edges of the object to avoid small
* sized over/underflows from neighboring allocations.
s->offset = ALIGN(size / 2, sizeof(void *));
s->offset = ALIGN(freepointer_area / 2, sizeof(void *));
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