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Sun, 02 Feb 2020 18:05:47 -0800 Received: from MTKMBS07N2.mediatek.inc (172.21.101.141) by MTKMBS62DR.mediatek.inc (172.29.94.18) with Microsoft SMTP Server (TLS) id 15.0.1395.4; Sun, 2 Feb 2020 18:05:45 -0800 Received: from mtkcas07.mediatek.inc (172.21.101.84) by mtkmbs07n2.mediatek.inc (172.21.101.141) with Microsoft SMTP Server (TLS) id 15.0.1395.4; Mon, 3 Feb 2020 10:05:06 +0800 Received: from [172.21.84.99] (172.21.84.99) by mtkcas07.mediatek.inc (172.21.101.73) with Microsoft SMTP Server id 15.0.1395.4 via Frontend Transport; Mon, 3 Feb 2020 10:05:30 +0800 Message-ID: <1580695544.17006.7.camel@mtksdccf07> Subject: Re: [PATCH v3] lib/stackdepot: Fix global out-of-bounds in stackdepot From: Walter Wu To: Alexander Potapenko Date: Mon, 3 Feb 2020 10:05:44 +0800 In-Reply-To: References: <20200130064430.17198-1-walter-zh.wu@mediatek.com> <1580436306.11126.16.camel@mtksdccf07> X-Mailer: Evolution 3.2.3-0ubuntu6 MIME-Version: 1.0 X-MTK: N X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200202_180552_819441_0ECAE807 X-CRM114-Status: GOOD ( 24.02 ) X-BeenThere: linux-mediatek@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kate Stewart , wsd_upstream , Greg Kroah-Hartman , LKML , linux-mediatek@lists.infradead.org, linux-arm-kernel@lists.infradead.org, Josh Poimboeuf , Matthias Brugger , Thomas Gleixner , Dmitry Vyukov Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "Linux-mediatek" Errors-To: linux-mediatek-bounces+linux-mediatek=archiver.kernel.org@lists.infradead.org On Fri, 2020-01-31 at 19:11 +0100, Alexander Potapenko wrote: > On Fri, Jan 31, 2020 at 3:05 AM Walter Wu wrote: > > > > On Thu, 2020-01-30 at 13:03 +0100, Alexander Potapenko wrote: > > > On Thu, Jan 30, 2020 at 7:44 AM Walter Wu wrote: > > > > > > Hi Walter, > > > > > > > If the depot_index = STACK_ALLOC_MAX_SLABS - 2 and next_slab_inited = 0, > > > > then it will cause array out-of-bounds access, so that we should modify > > > > the detection to avoid this array out-of-bounds bug. > > > > > > > > Assume depot_index = STACK_ALLOC_MAX_SLABS - 3 > > > > Consider following call flow sequence: > > > > > > > > stack_depot_save() > > > > depot_alloc_stack() > > > > if (unlikely(depot_index + 1 >= STACK_ALLOC_MAX_SLABS)) //pass > > > > depot_index++ //depot_index = STACK_ALLOC_MAX_SLABS - 2 > > > > if (depot_index + 1 < STACK_ALLOC_MAX_SLABS) //enter > > > > smp_store_release(&next_slab_inited, 0); //next_slab_inited = 0 > > > > init_stack_slab() > > > > if (stack_slabs[depot_index] == NULL) //enter and exit > > > > > > > > stack_depot_save() > > > > depot_alloc_stack() > > > > if (unlikely(depot_index + 1 >= STACK_ALLOC_MAX_SLABS)) //pass > > > > depot_index++ //depot_index = STACK_ALLOC_MAX_SLABS - 1 > > > > init_stack_slab(&prealloc) > > > > stack_slabs[depot_index + 1] //here get global out-of-bounds > > > > > > > > Cc: Dmitry Vyukov > > > > Cc: Matthias Brugger > > > > Cc: Thomas Gleixner > > > > Cc: Alexander Potapenko > > > > Cc: Josh Poimboeuf > > > > Cc: Kate Stewart > > > > Cc: Greg Kroah-Hartman > > > > Cc: Kate Stewart > > > > Signed-off-by: Walter Wu > > > > --- > > > > changes in v2: > > > > modify call flow sequence and preconditon > > > > > > > > changes in v3: > > > > add some reviewers > > > > --- > > > > lib/stackdepot.c | 2 +- > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > diff --git a/lib/stackdepot.c b/lib/stackdepot.c > > > > index ed717dd08ff3..7e8a15e41600 100644 > > > > --- a/lib/stackdepot.c > > > > +++ b/lib/stackdepot.c > > > > @@ -106,7 +106,7 @@ static struct stack_record *depot_alloc_stack(unsigned long *entries, int size, > > > > required_size = ALIGN(required_size, 1 << STACK_ALLOC_ALIGN); > > > > > > > > if (unlikely(depot_offset + required_size > STACK_ALLOC_SIZE)) { > > > > - if (unlikely(depot_index + 1 >= STACK_ALLOC_MAX_SLABS)) { > > > > + if (unlikely(depot_index + 2 >= STACK_ALLOC_MAX_SLABS)) { > > This again means stack_slabs[STACK_ALLOC_MAX_SLABS - 2] gets > initialized, but stack_slabs[STACK_ALLOC_MAX_SLABS - 1] doesn't, > because we'll be bailing out from init_stack_slab() from now on. > Does this patch actually fix the problem (do you have a reliable reproducer?) We get it by reviewing code, because Kasan doesn't scan it and we catch another bug internally, we found it unintentionally. > This addition of 2 is also counterintuitive, I don't think further > readers will understand the logic behind it. > Yes > What if we just check that depot_index + 1 is a valid index before accessing it? > It should fix the problem, do you want to send this patch? > diff --git a/lib/stackdepot.c b/lib/stackdepot.c > index 2e7d2232ed3c..c2e6ff18d716 100644 > --- a/lib/stackdepot.c > +++ b/lib/stackdepot.c > @@ -106,7 +106,9 @@ static bool init_stack_slab(void **prealloc) > if (stack_slabs[depot_index] == NULL) { > stack_slabs[depot_index] = *prealloc; > } else { > - stack_slabs[depot_index + 1] = *prealloc; > + /* If this is the last depot slab, do not touch the next one. */ > + if (depot_index + 1 < STACK_ALLOC_MAX_SLABS) > + stack_slabs[depot_index + 1] = *prealloc; > /* > * This smp_store_release pairs with smp_load_acquire() from > * |next_slab_inited| above and in stack_depot_save(). _______________________________________________ Linux-mediatek mailing list Linux-mediatek@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-mediatek