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 89689C71157 for ; Tue, 17 Jun 2025 08:18:37 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id DC1F06B0089; Tue, 17 Jun 2025 04:18:36 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D77E96B008A; Tue, 17 Jun 2025 04:18:36 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CAF306B0092; Tue, 17 Jun 2025 04:18:36 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id B8EB36B0089 for ; Tue, 17 Jun 2025 04:18:36 -0400 (EDT) Received: from smtpin14.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 7119C10208A for ; Tue, 17 Jun 2025 08:18:36 +0000 (UTC) X-FDA: 83564191032.14.303F115 Received: from out-182.mta1.migadu.com (out-182.mta1.migadu.com [95.215.58.182]) by imf29.hostedemail.com (Postfix) with ESMTP id 89409120009 for ; Tue, 17 Jun 2025 08:18:34 +0000 (UTC) Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b="FDckDr/M"; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf29.hostedemail.com: domain of lance.yang@linux.dev designates 95.215.58.182 as permitted sender) smtp.mailfrom=lance.yang@linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1750148314; a=rsa-sha256; cv=none; b=LXeOmt6DR01EENDY5UU1aNlUUNNlaWN1yPvIzPyyMGxxD2BN2GZuzjE1A1nS/NF2fqVqrO QEs4dw6Gv/uRQeWP2vwoYTa6xregeCFA8djVM/RXdx04DGkSmrhGSHO0ibsfODvHT6msrm RuAsVkbV8INpHTsTPgi3QQ5SknzMPkg= ARC-Authentication-Results: i=1; imf29.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b="FDckDr/M"; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf29.hostedemail.com: domain of lance.yang@linux.dev designates 95.215.58.182 as permitted sender) smtp.mailfrom=lance.yang@linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1750148314; 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=A1FkqVxwYvuLbKfximV4nOd1sO0YqsqNdMqotcHBlZM=; b=viLIdb5oia3YSotM9ioZ8Uta8pCJGqY5IV8kvj55LHmvFuUHUqO56FKl9G1rm4Xlv++Nap pN9wwyDcUkUsyaarlDdO6Z3ydjh3gXodtNqQgDYsq1tOM8QPrMH5DQnGhEN7hhWekNinmv ZLzwhLxMZ7/XRErDm7KdLWVTzWbyvXI= Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1750148312; 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=A1FkqVxwYvuLbKfximV4nOd1sO0YqsqNdMqotcHBlZM=; b=FDckDr/MWkYDaipG5ywk10/+fpoBjYB42eVALTmxU/dwb9jHjKcl5xlSyC5+QquG86xjw3 9DrjYYcQ072iMnp5ypIUpz8bfvSGeB+0JURWS9BxHh8pytjIA5eL8w0m5d4Ebe5wDbtr8M BlGA/RFHlPgPG68Tj33Nb5Obgt7Ww6k= Date: Tue, 17 Jun 2025 16:18:24 +0800 MIME-Version: 1.0 Subject: Re: [PATCH 1/1] mm/madvise: initialize prev pointer in madvise_walk_vmas Content-Language: en-US To: David Hildenbrand Cc: 21cnbao@gmail.com, Liam.Howlett@oracle.com, vbabka@suse.cz, jannh@google.com, lorenzo.stoakes@oracle.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, Lance Yang References: <20250617020544.57305-1-lance.yang@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam01 X-Stat-Signature: i4ymefmqamiqtkcbtfznijzixd88csj8 X-Rspamd-Queue-Id: 89409120009 X-Rspam-User: X-HE-Tag: 1750148314-637458 X-HE-Meta: U2FsdGVkX194RCR8fggTC/XgxrS/1XF2imhVqkBNeyydAeR/v7gvR+1JgCM+nNnJJe7n6eirF8ubXNmTvtyyyto/qpyqWiN1aypyntlTIRLnAGY6dTOjF1kYVha7Qw+ChnTdEgcMGfUaHmeU6ZhIbyv9doPb9oCDrCZuaFxXE1lJ1p3CQfVitY+XBTMV/I4M5Xbab9WZy3eAjdAef87cPlx5ACSwmEljdW7h1Ov6r72QTUp6/uR+XmgZjZtc8Hq6u8Eb+rFd4VFqMyWbFusIEl67IDbgelmgketKXXtutGXAK5kID0lvVXxCP6Riz0P6dLyUJuS67QeYflP4MuMrfXVXLZFwmtC4iGLF9MZVfqhIH8uHE1lGlonutvnaop0mi2UVwTZxHg5hsqnDkwcOWb0BSrCmV0rKBEjCKcVutZ3LUbxQaiAgJMJITd3cpDzP7+goipfNLfIXydXPuEsLzqHLPIP5e1nOJjH68uo4YhtQQrAFRCBh5IjVr+JgoSG1m41vdNqAEGKeKOg9PwJ0iR0bP2OxCNqXnSVdQ3yRnVAHXVvHKlK4KGavhoK+MnS5NdwRNQC+Zm8AsecG7aVmAjtRZmv37ZpASCKKMbiac9M0F6EcN8m1Pm2TDVK+LUwOc7LICK1ZkSeWVi+tRLhNvEr0AcubaYkoIm3P2hcABY9po4u4Fp6q4rjpr7hioNBeIIk/NgJcFecDR2spfFimhUJ/NC7lsB8PZX5HF7p1LXQyHgCKmbhzPLjuTWjC4lHGcBH07LnA+xIbZAB0qAGJniJuQyFc9gNRqXhBvjlq2pUxjKjbjTzR9I94OqOYcQTw7J8PeT6W5enp1KMIrKZzay4+P1Lg4EfrUgQcBHCImpOnrZD62fYyp3l2h9IvAVKn4CceN3nvvS1UZABuC3qik6RwJln/AxFx0lOjuMnfO2BbuboBkr2EmuaxyNBBTjhrOvemZ4YdRnsl8poLRGX fWxZ5sK8 Brx3p/YE9Ik16HSB8D2k+40Q3jRurhJExIMNS4xhsBFqRCWdtPtPZo/DWiKmuswaCBdr1wHdAtR7NsrqndqF3tS8oJnnBl5oxq16qtpcPE5ch8XfVh3kagrsanKerz74bmA1NhLNFAwkBl4nB3UeqKNpM/ZNWY1ORvIVmUUQIj1s8oeD4Qet4T5AjwRo7xkJlEucrNh4dpMcKpbdh9B0qoJPTTzo5J4QtzzEs9KoocudsOymR/iIaLYstoRsrtMQs+bJe2i2drQFaK30LxduNNYzFESIDCQlAoZo508Enk7EKmR43DXT+vhSKrjCKIyo4V+ci 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 15:54, David Hildenbrand wrote: > On 17.06.25 04:05, 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. > > So, we are passing the pointer value to visit(), which is not undefined > behavior. > > The issue would be if anybody takes a look at the value stored at that > pointer. Because, already passing an uninitialized value to a (non- > inlined) function is undefined behavior according to C. Yes, that is precisely is what I am concerned about ;) > > In madvise_update_vma()->vma_modify_flags_name() we do exactly that, > correct? > >     vma = vma_modify_flags_name(&vmi, *prev, ... > > We should use Fixes: then. Exactly, I missed that. Will add the "Fixes" tag and send out a new version. > > > Acked-by: David Hildenbrand Thanks! Lance > >> >> 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; >>       /* > >