From patchwork Wed Jul 7 01:29:19 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Siddhesh Poyarekar X-Patchwork-Id: 44196 Return-Path: X-Original-To: patchwork@sourceware.org Delivered-To: patchwork@sourceware.org Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id 75B94393BC2B for ; Wed, 7 Jul 2021 01:29:59 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 75B94393BC2B DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1625621399; bh=wrI/rrGoS+dyIe8RtSyXRLeyGKrp1M6U4yo2Go5X17Y=; h=To:Subject:Date:List-Id:List-Unsubscribe:List-Archive:List-Post: List-Help:List-Subscribe:From:Reply-To:Cc:From; b=cN7u4fVOnbOd42Zb0TY0EcidN5PPIB1oSP0pNlrdS4PlqenWpf69Gp/IL5IP7dakd T1nM6tIc6Apj/ad6T+STz9g/Mr0M/mh0y0kChqCY8S2CRvTz36fBCxpvhmW+4qN+Yu JsW000UjgNa2pj6fiZGkAHIXXJajLiJhgsugAFso= X-Original-To: libc-alpha@sourceware.org Delivered-To: libc-alpha@sourceware.org Received: from camel.birch.relay.mailchannels.net (camel.birch.relay.mailchannels.net [23.83.209.29]) by sourceware.org (Postfix) with ESMTPS id AE9E8385743E for ; Wed, 7 Jul 2021 01:29:36 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org AE9E8385743E X-Sender-Id: dreamhost|x-authsender|siddhesh@gotplt.org Received: from relay.mailchannels.net (localhost [127.0.0.1]) by relay.mailchannels.net (Postfix) with ESMTP id C07257E21E3; Wed, 7 Jul 2021 01:29:34 +0000 (UTC) Received: from pdx1-sub0-mail-a15.g.dreamhost.com (100-105-161-168.trex-nlb.outbound.svc.cluster.local [100.105.161.168]) (Authenticated sender: dreamhost) by relay.mailchannels.net (Postfix) with ESMTPA id 081797E2122; Wed, 7 Jul 2021 01:29:34 +0000 (UTC) X-Sender-Id: dreamhost|x-authsender|siddhesh@gotplt.org Received: from pdx1-sub0-mail-a15.g.dreamhost.com (pop.dreamhost.com [64.90.62.162]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384) by 100.105.161.168 (trex/6.3.3); Wed, 07 Jul 2021 01:29:34 +0000 X-MC-Relay: Neutral X-MailChannels-SenderId: dreamhost|x-authsender|siddhesh@gotplt.org X-MailChannels-Auth-Id: dreamhost X-Eyes-Relation: 36e4e1a469e25e3c_1625621374322_3518060375 X-MC-Loop-Signature: 1625621374321:590764776 X-MC-Ingress-Time: 1625621374321 Received: from pdx1-sub0-mail-a15.g.dreamhost.com (localhost [127.0.0.1]) by pdx1-sub0-mail-a15.g.dreamhost.com (Postfix) with ESMTP id C3DF38A26E; Tue, 6 Jul 2021 18:29:33 -0700 (PDT) Received: from rhbox.intra.reserved-bit.com (unknown [1.186.101.110]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) (Authenticated sender: siddhesh@gotplt.org) by pdx1-sub0-mail-a15.g.dreamhost.com (Postfix) with ESMTPSA id 2C8CE8A2B9; Tue, 6 Jul 2021 18:29:30 -0700 (PDT) X-DH-BACKEND: pdx1-sub0-mail-a15 To: libc-alpha@sourceware.org Subject: [PATCH] Harden tcache double-free check Date: Wed, 7 Jul 2021 06:59:19 +0530 Message-Id: <20210707012919.1298612-1-siddhesh@sourceware.org> X-Mailer: git-send-email 2.31.1 MIME-Version: 1.0 X-Spam-Status: No, score=-3494.3 required=5.0 tests=BAYES_00, GIT_PATCH_0, JMQ_SPF_NEUTRAL, KAM_DMARC_NONE, KAM_DMARC_STATUS, RCVD_IN_BARRACUDACENTRAL, RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H2, SPF_HELO_NONE, SPF_NEUTRAL, TXREP autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-Patchwork-Original-From: Siddhesh Poyarekar via Libc-alpha From: Siddhesh Poyarekar Reply-To: Siddhesh Poyarekar Cc: fweimer@redhat.com, Eyal Itkin Errors-To: libc-alpha-bounces+patchwork=sourceware.org@sourceware.org Sender: "Libc-alpha" The tcache allocator layer uses the tcache pointer as a key to identify a block that may be freed twice. Since this is in the application data area, an attacker exploiting a use-after-free could potentially get access to the entire tcache structure through this key. A detailed write-up was provided by Awarau here: https://awaraucom.wordpress.com/2020/07/19/house-of-io-remastered/ Replace this static pointer use for key checking with one that is generated at malloc initialization. The first attempt is through getrandom with a fallback to random_bits(), which is a simple pseudo-random number generator based on the clock. The fallback ought to be sufficient since the goal of the randomness is only to make the key arbitrary enough that it is very unlikely to collide with user data. Co-authored-by: Eyal Itkin --- malloc/arena.c | 8 ++++++++ malloc/malloc.c | 32 ++++++++++++++++++++++++++++---- 2 files changed, 36 insertions(+), 4 deletions(-) diff --git a/malloc/arena.c b/malloc/arena.c index 7eb110445e..991fc21a7e 100644 --- a/malloc/arena.c +++ b/malloc/arena.c @@ -287,6 +287,10 @@ extern struct dl_open_hook *_dl_open_hook; libc_hidden_proto (_dl_open_hook); #endif +#if USE_TCACHE +static void tcache_key_initialize (void); +#endif + static void ptmalloc_init (void) { @@ -295,6 +299,10 @@ ptmalloc_init (void) __malloc_initialized = 0; +#if USE_TCACHE + tcache_key_initialize (); +#endif + #ifdef USE_MTAG if ((TUNABLE_GET_FULL (glibc, mem, tagging, int32_t, NULL) & 1) != 0) { diff --git a/malloc/malloc.c b/malloc/malloc.c index bb9a1642aa..68dc18dd03 100644 --- a/malloc/malloc.c +++ b/malloc/malloc.c @@ -252,6 +252,10 @@ #include +/* For tcache double-free check. */ +#include +#include + /* Debugging: @@ -3091,7 +3095,7 @@ typedef struct tcache_entry { struct tcache_entry *next; /* This field exists to detect double frees. */ - struct tcache_perthread_struct *key; + uintptr_t key; } tcache_entry; /* There is one of these for each thread, which contains the @@ -3108,6 +3112,26 @@ typedef struct tcache_perthread_struct static __thread bool tcache_shutting_down = false; static __thread tcache_perthread_struct *tcache = NULL; +/* Process-wide key to try and catch a double-free in the same thread. */ +static uintptr_t tcache_key; + +/* The value of tcache_key does not really have to be a cryptographically + secure random number. It only needs to be arbitrary enough so that it does + not collide with values present in applications, which would be quite rare, + about 1 in 2^wordsize. */ +static void +tcache_key_initialize (void) +{ + if (__getrandom (&tcache_key, sizeof(tcache_key), GRND_NONBLOCK) + != sizeof (tcache_key)) + { + tcache_key = random_bits (); +#if __WORDSIZE == 64 + tcache_key = (tcache_key << 32) | random_bits (); +#endif + } +} + /* Caller must ensure that we know tc_idx is valid and there's room for more chunks. */ static __always_inline void @@ -3117,7 +3141,7 @@ tcache_put (mchunkptr chunk, size_t tc_idx) /* Mark this chunk as "in the tcache" so the test in _int_free will detect a double free. */ - e->key = tcache; + e->key = tcache_key; e->next = PROTECT_PTR (&e->next, tcache->entries[tc_idx]); tcache->entries[tc_idx] = e; @@ -3134,7 +3158,7 @@ tcache_get (size_t tc_idx) malloc_printerr ("malloc(): unaligned tcache chunk detected"); tcache->entries[tc_idx] = REVEAL_PTR (e->next); --(tcache->counts[tc_idx]); - e->key = NULL; + e->key = 0; return (void *) e; } @@ -4437,7 +4461,7 @@ _int_free (mstate av, mchunkptr p, int have_lock) trust it (it also matches random payload data at a 1 in 2^ chance), so verify it's not an unlikely coincidence before aborting. */ - if (__glibc_unlikely (e->key == tcache)) + if (__glibc_unlikely (e->key == tcache_key)) { tcache_entry *tmp; size_t cnt = 0;