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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id r4sm566043pgp.60.2020.06.17.12.53.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 17 Jun 2020 12:53:53 -0700 (PDT) From: Kees Cook To: Andrew Morton Cc: Kees Cook , Vlastimil Babka , Roman Gushchin , Christoph Lameter , Alexander Popov , Pekka Enberg , David Rientjes , Joonsoo Kim , vinmenon@codeaurora.org, Matthew Garrett , Jann Horn , Vijayanand Jitta , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH 2/2] slab: Add naive detection of double free Date: Wed, 17 Jun 2020 12:53:49 -0700 Message-Id: <20200617195349.3471794-3-keescook@chromium.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20200617195349.3471794-1-keescook@chromium.org> References: <20200617195349.3471794-1-keescook@chromium.org> MIME-Version: 1.0 X-Rspamd-Queue-Id: A6BD220001569C82 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 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: Similar to commit ce6fa91b9363 ("mm/slub.c: add a naive detection of double free or corruption"), add a very cheap double-free check for SLAB under CONFIG_SLAB_FREELIST_HARDENED. With this added, the "SLAB_FREE_DOUBLE" LKDTM test passes under SLAB: lkdtm: Performing direct entry SLAB_FREE_DOUBLE lkdtm: Attempting double slab free ... ------------[ cut here ]------------ WARNING: CPU: 2 PID: 2193 at mm/slab.c:757 ___cache _free+0x325/0x390 Signed-off-by: Kees Cook --- mm/slab.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/mm/slab.c b/mm/slab.c index 9350062ffc1a..c4e3a194b271 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -749,6 +749,16 @@ static void drain_alien_cache(struct kmem_cache *cac= hep, } } =20 +/* &alien->lock must be held by alien callers. */ +static __always_inline void __free_one(struct array_cache *ac, void *obj= p) +{ + /* Avoid trivial double-free. */ + if (IS_ENABLED(CONFIG_SLAB_FREELIST_HARDENED) && + WARN_ON_ONCE(ac->avail > 0 && ac->entry[ac->avail - 1] =3D=3D objp)= ) + return; + ac->entry[ac->avail++] =3D objp; +} + static int __cache_free_alien(struct kmem_cache *cachep, void *objp, int node, int page_node) { @@ -767,7 +777,7 @@ static int __cache_free_alien(struct kmem_cache *cach= ep, void *objp, STATS_INC_ACOVERFLOW(cachep); __drain_alien_cache(cachep, ac, page_node, &list); } - ac->entry[ac->avail++] =3D objp; + __free_one(ac, objp); spin_unlock(&alien->lock); slabs_destroy(cachep, &list); } else { @@ -3466,7 +3476,7 @@ void ___cache_free(struct kmem_cache *cachep, void = *objp, } } =20 - ac->entry[ac->avail++] =3D objp; + __free_one(ac, objp); } =20 /** --=20 2.25.1