From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 03D40C71136 for ; Tue, 17 Jun 2025 09:21:15 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 845A96B007B; Tue, 17 Jun 2025 05:21:14 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 7CFA76B0088; Tue, 17 Jun 2025 05:21:14 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6EC2C6B0089; Tue, 17 Jun 2025 05:21:14 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 5A9F76B007B for ; Tue, 17 Jun 2025 05:21:14 -0400 (EDT) Received: from smtpin14.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 0EDA9141B0C for ; Tue, 17 Jun 2025 09:21:14 +0000 (UTC) X-FDA: 83564348868.14.B761411 Received: from out-184.mta0.migadu.com (out-184.mta0.migadu.com [91.218.175.184]) by imf05.hostedemail.com (Postfix) with ESMTP id 3301E10000A for ; Tue, 17 Jun 2025 09:21:11 +0000 (UTC) Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=Dd6FDGyg; spf=pass (imf05.hostedemail.com: domain of lance.yang@linux.dev designates 91.218.175.184 as permitted sender) smtp.mailfrom=lance.yang@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1750152072; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=R7X3zKdDa6C/f9djBhnhvhmD9Fs51aNtXIyVNL1VTRk=; b=JKOLMqAih2md7fFfiyjy+t0H7n4SkM7sxqUXFz28OSwHES6qY3SqBAnwQ/Y/UHzAXlT2Vu ecKYSmXRnfsb08itZJQsvcO6OKyOvvn+cmvE0yCK+gNQbAIN37asDZzwGiVmAfee2hojmG WY4NKOPmkmqR/fCgqcozHBRBKYf2lOY= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1750152072; a=rsa-sha256; cv=none; b=xwdRtcOhKVJFBT8dV51b9Hrvw8Z/qYBY7E+Kz6x2656bgmpfdKxcms/3uGWGif9UHvy9H+ Zrtay7i16L0ui30lja0EOI6JHm7bI8udBxFInry3fub5Wn6tkrhmgcSOAXqKadnY1tp7EK m8iEEuJdbW95rkSS9dE68VOd8fJXbMw= ARC-Authentication-Results: i=1; imf05.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=Dd6FDGyg; spf=pass (imf05.hostedemail.com: domain of lance.yang@linux.dev designates 91.218.175.184 as permitted sender) smtp.mailfrom=lance.yang@linux.dev; dmarc=pass (policy=none) header.from=linux.dev Message-ID: <142cb257-6c04-4a8f-9153-4759c50aff4e@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1750152068; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=R7X3zKdDa6C/f9djBhnhvhmD9Fs51aNtXIyVNL1VTRk=; b=Dd6FDGygEjufLhqJ9Z2/eOK4jp/IHSPlY3m5/IVJQmj1cgBIsMiDOIK679YmM/lxK1ekB4 /I7zRM9rZTaQYTK+glOlivsdq9XXfgqOkYJUFgOYrENTLXNBtqUdRr/vty+CPcPhGC9x5c PvcfiWXfd3FBbEkTNvNZ8GjfRTL1Trc= Date: Tue, 17 Jun 2025 17:21:03 +0800 MIME-Version: 1.0 Subject: Re: [PATCH 1/1] mm/madvise: initialize prev pointer in madvise_walk_vmas Content-Language: en-US To: Lorenzo Stoakes Cc: akpm@linux-foundation.org, 21cnbao@gmail.com, david@redhat.com, Liam.Howlett@oracle.com, vbabka@suse.cz, jannh@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Lance Yang References: <20250617020544.57305-1-lance.yang@linux.dev> <6181fd25-6527-4cd0-b67f-2098191d262d@lucifer.local> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: <6181fd25-6527-4cd0-b67f-2098191d262d@lucifer.local> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 3301E10000A X-Stat-Signature: 4ixwuhmmxcpeyh5rbty5s57geqxmyh74 X-HE-Tag: 1750152071-234049 X-HE-Meta: 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 /rJO2vbw EYPOMFtrJSZDyP9dCxHOK92CuzKkeD2F7DG6rb3pvkTSDHVLvGJCTsZUv/5gwZdmmP38MabYrVbBzoN6kJ7+32U2N35dhna3U9ZjbBFcnqzA3FurSyOnVP13vyeoE8C2jtdByVwb5djQ/4uqh3/w65IDi2Fi0CS8h/GS4scKGjYdpbU/rR6EJAKp2VA0AldnXpS26gnHA2niALFopgZdDEgcRVib5MxdwjyT5uiDPwqN9Cr0r/NHRYtJTFFc/fgJORIplJKlTa1c4O+z3udIYZCG9SgriFgV+F8PP5O5K7f7qTCFtm69PDmxCbWqz8Q3nff9c/Td20+BUMaOvSK2zNNVTfg== 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: List-Subscribe: List-Unsubscribe: On 2025/6/17 16:50, Lorenzo Stoakes wrote: > Lace - To simplify and not get bogged down in sub-threads am replying at the top > level. > > TL;DR this fix is incorrect, but the issue is correct :) > > So the patch at [0] introduced by Barry changed things in a way that _appears_ > broken but in fact aren't, however we should do something about this, obviously. > > That patch added: > > if (madv_behavior && madv_behavior->lock_mode == MADVISE_VMA_READ_LOCK) { > vma = try_vma_read_lock(mm, madv_behavior, start, end); > if (vma) { > error = visit(vma, &prev, start, end, arg); > vma_end_read(vma); > return error; > } > } > > And the problem is, in this case, we don't initialise prev. > > In all other cases, we do (under mmap lock): > > vma = find_vma_prev(mm, start, &prev); > if (vma && start > vma->vm_start) > prev = vma; > > The reason this isn't a problem is that the only madvise operation that > currently supports this, madvise_dontneed_free() will initialise *prev = vma. > > BUT we really shouldn't be relying on this, so I attach a fixpatch. > > Given Barry's patch isn't mainline yet, I think this should just be squashed > into that as a fix? > > It kind of sucks to do this, but it resolves any potential bug. > > I think a follow up is needed, as there's an implicit assumption it seems that > prev is updated immediately for most callers, but of course anon_vma_name is a > special snowflake. > > todos++; Ah, please keep me in the loop ;) > > Lance - I suggest you reply to Barry's series with the below fix, or I can if > you prefer? Sure, go ahead! Thanks, Lance > > [0]: https://lore.kernel.org/linux-mm/20250607220150.2980-1-21cnbao@gmail.com/ > > Thanks! > > On Tue, Jun 17, 2025 at 10:05:43AM +0800, Lance Yang wrote: >> From: Lance Yang >> >> The prev pointer was uninitialized, which could lead to undefined behavior >> where its address is taken and passed to the visit() callback without being >> assigned a value. >> >> Initializing it to NULL makes the code safer and prevents potential bugs >> if a future callback function attempts to read from it. >> >> Signed-off-by: Lance Yang >> --- >> mm/madvise.c | 4 ++-- >> 1 file changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/mm/madvise.c b/mm/madvise.c >> index 267d8e4adf31..c87325000303 100644 >> --- a/mm/madvise.c >> +++ b/mm/madvise.c >> @@ -1536,10 +1536,10 @@ int madvise_walk_vmas(struct mm_struct *mm, unsigned long start, >> struct vm_area_struct **prev, unsigned long start, >> unsigned long end, void *arg)) >> { >> + struct vm_area_struct *prev = NULL; >> struct vm_area_struct *vma; >> - struct vm_area_struct *prev; >> - unsigned long tmp; >> int unmapped_error = 0; >> + unsigned long tmp; >> int error; >> >> /* >> -- >> 2.49.0 >> > > ----8<---- > From c8dc9f5b2929e389cac44b79201fff43e0ab8195 Mon Sep 17 00:00:00 2001 > From: Lorenzo Stoakes > Date: Tue, 17 Jun 2025 09:46:27 +0100 > Subject: [PATCH] fix > > Signed-off-by: Lorenzo Stoakes > --- > mm/madvise.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/mm/madvise.c b/mm/madvise.c > index 267d8e4adf31..45ea4588e34e 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -1549,6 +1549,7 @@ int madvise_walk_vmas(struct mm_struct *mm, unsigned long start, > if (madv_behavior && madv_behavior->lock_mode == MADVISE_VMA_READ_LOCK) { > vma = try_vma_read_lock(mm, madv_behavior, start, end); > if (vma) { > + *prev = vma; > error = visit(vma, &prev, start, end, arg); > vma_end_read(vma); > return error; > -- > 2.49.0