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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id w143sm11701672pfc.31.2020.10.09.12.54.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 09 Oct 2020 12:54:16 -0700 (PDT) From: Kees Cook To: Andrew Morton Cc: Kees Cook , stable@vger.kernel.org, Marco Elver , Jonathan Corbet , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Vlastimil Babka , Roman Gushchin , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v2 2/3] mm/slub: Fix redzoning for small allocations Date: Fri, 9 Oct 2020 12:54:10 -0700 Message-Id: <20201009195411.4018141-3-keescook@chromium.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20201009195411.4018141-1-keescook@chromium.org> References: <20201009195411.4018141-1-keescook@chromium.org> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: The redzone area for SLUB exists between s->object_size and s->inuse (which is at least the word-aligned object size). If a cache were created with an object_size smaller than sizeof(void *), the in-object stored freelist pointer will be overwritten by redzoning (e.g. with boot param "slub_debug=3DZV"): BUG test (Tainted: G B ): Right Redzone overwritten -------------------------------------------------------------------------= ---- INFO: 0xffff957ead1c05de-0xffff957ead1c05df @offset=3D1502. First byte 0x= 1a instead of 0xbb INFO: Slab 0xffffef3950b47000 objects=3D170 used=3D170 fp=3D0x00000000000= 00000 flags=3D0x8000000000000200 INFO: Object 0xffff957ead1c05d8 @offset=3D1496 fp=3D0xffff957ead1c0620 Redzone (____ptrval____): bb bb bb bb bb bb bb bb ........ Object (____ptrval____): f6 f4 a5 40 1d e8 ...@.. Redzone (____ptrval____): 1a aa .. Padding (____ptrval____): 00 00 00 00 00 00 00 00 ........ Store the freelist pointer out of line when object_size is smaller than sizeof(void *) and redzoning is enabled. (Note that no caches with such a size are known to exist in the kernel currently.) Fixes: 81819f0fc828 ("SLUB core") Cc: stable@vger.kernel.org Signed-off-by: Kees Cook --- mm/slub.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index f4f1d63f0ab9..752fad36522c 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -3682,15 +3682,17 @@ static int calculate_sizes(struct kmem_cache *s, = int forced_order) */ s->inuse =3D size; =20 - if (((flags & (SLAB_TYPESAFE_BY_RCU | SLAB_POISON)) || - s->ctor)) { + if ((flags & (SLAB_TYPESAFE_BY_RCU | SLAB_POISON)) || + ((flags & SLAB_RED_ZONE) && s->object_size < sizeof(void *)) || + s->ctor) { /* * Relocate free pointer after the object if it is not * permitted to overwrite the first word of the object on * kmem_cache_free. * * This is the case if we do RCU, have a constructor or - * destructor or are poisoning the objects. + * destructor, are poisoning the objects, or are + * redzoning an object smaller than sizeof(void *). * * The assumption that s->offset >=3D s->inuse means free * pointer is outside of the object is used in the --=20 2.25.1