From: Waiman Long longman@redhat.com
[ Upstream commit cbfc35a48609ceac978791e3ab9dde0c01f8cb20 ]
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.
============================================================================= 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: 3202fa62fb43 ("slub: relocate freelist pointer to middle of object") Signed-off-by: Waiman Long longman@redhat.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Reviewed-by: Matthew Wilcox (Oracle) willy@infradead.org Reviewed-by: Kees Cook keescook@chromium.org Acked-by: Rafael 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: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- mm/slub.c | 45 ++++++++++++++++++++++++++++++--------------- 1 file changed, 30 insertions(+), 15 deletions(-)
diff --git a/mm/slub.c b/mm/slub.c index 822ba07245291..d69934eac9e94 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -533,15 +533,32 @@ 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; } @@ -682,10 +699,7 @@ 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); @@ -776,7 +790,7 @@ 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) @@ -810,11 +824,7 @@ 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 */ @@ -900,7 +910,7 @@ 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. @@ -3585,6 +3595,11 @@ 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 *);