From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: [patch 09/15] mm/slub: fix incorrect interpretation of s->offset Date: Thu, 07 May 2020 18:36:06 -0700 Message-ID: <20200508013606.8RolOfSw-%akpm@linux-foundation.org> References: <20200507183509.c5ef146c5aaeb118a25a39a8@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Return-path: Received: from mail.kernel.org ([198.145.29.99]:58660 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726514AbgEHBgI (ORCPT ); Thu, 7 May 2020 21:36:08 -0400 In-Reply-To: <20200507183509.c5ef146c5aaeb118a25a39a8@linux-foundation.org> Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: akpm@linux-foundation.org, aquini@redhat.com, changbin.du@gmail.com, cl@linux.com, iamjoonsoo.kim@lge.com, keescook@chromium.org, linux-mm@kvack.org, longman@redhat.com, Markus.Elfring@web.de, mm-commits@vger.kernel.org, penberg@kernel.org, rientjes@google.com, silvio.cesare@gmail.com, torvalds@linux-foundation.org, vnik@duasynt.com, willy@infradead.org From: Waiman Long Subject: 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 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_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). Link: http://lkml.kernel.org/r/20200429135328.26976-1-longman@redhat.com Fixes: 3202fa62fb43 ("slub: relocate freelist pointer to middle of object") Signed-off-by: Waiman Long Reviewed-by: Matthew Wilcox (Oracle) Acked-by: Rafael Aquini Reviewed-by: Kees Cook Cc: Christoph Lameter Cc: Vitaly Nikolenko Cc: Silvio Cesare Cc: Christoph Lameter Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Cc: Markus Elfring Cc: Changbin Du Signed-off-by: Andrew Morton --- mm/slub.c | 45 ++++++++++++++++++++++++++++++--------------- 1 file changed, 30 insertions(+), 15 deletions(-) --- a/mm/slub.c~mm-slub-fix-incorrect-interpretation-of-s-offset +++ a/mm/slub.c @@ -551,15 +551,32 @@ static void print_section(char *level, c 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_ca 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 * 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 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_cach 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_c * * 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 *); _