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Date:   Tue,  3 May 2022 18:44:31 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Gustavo A . R . Silva" <gustavoars@...nel.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Russell King <linux@...linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Muchun Song <songmuchun@...edance.com>,
        linux-arm-kernel@...ts.infradead.org,
        Alexei Starovoitov <ast@...nel.org>,
        alsa-devel@...a-project.org, Al Viro <viro@...iv.linux.org.uk>,
        Andrew Gabbasov <andrew_gabbasov@...tor.com>,
        Andy Gross <agross@...nel.org>,
        Andy Lavr <andy.lavr@...il.com>,
        Arend van Spriel <aspriel@...il.com>,
        Baowen Zheng <baowen.zheng@...igine.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Bradley Grove <linuxdrivers@...otech.com>,
        brcm80211-dev-list.pdl@...adcom.com,
        Christian Göttsche <cgzones@...glemail.com>,
        Christian Lamparter <chunkeey@...glemail.com>,
        Chris Zankel <chris@...kel.net>,
        Cong Wang <cong.wang@...edance.com>,
        Daniel Axtens <dja@...ens.net>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Dan Williams <dan.j.williams@...el.com>,
        David Gow <davidgow@...gle.com>,
        David Howells <dhowells@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>,
        devicetree@...r.kernel.org, Dexuan Cui <decui@...rosoft.com>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        Eli Cohen <elic@...dia.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Paris <eparis@...isplace.org>,
        Eugeniu Rosca <erosca@...adit-jv.com>,
        Felipe Balbi <balbi@...nel.org>,
        Francis Laniel <laniel_francis@...vacyrequired.com>,
        Frank Rowand <frowand.list@...il.com>,
        Franky Lin <franky.lin@...adcom.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Gregory Greenman <gregory.greenman@...el.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Hante Meuleman <hante.meuleman@...adcom.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Hulk Robot <hulkci@...wei.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        James Morris <jmorris@...ei.org>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Jason Gunthorpe <jgg@...pe.ca>, Jens Axboe <axboe@...nel.dk>,
        Johan Hedberg <johan.hedberg@...il.com>,
        Johannes Berg <johannes.berg@...el.com>,
        Johannes Berg <johannes@...solutions.net>,
        John Keeping <john@...anate.com>,
        Juergen Gross <jgross@...e.com>, Kalle Valo <kvalo@...nel.org>,
        Keith Packard <keithp@...thp.com>, keyrings@...r.kernel.org,
        kunit-dev@...glegroups.com,
        Kuniyuki Iwashima <kuniyu@...zon.co.jp>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Lee Jones <lee.jones@...aro.org>,
        Leon Romanovsky <leon@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        linux1394-devel@...ts.sourceforge.net,
        linux-afs@...ts.infradead.org, linux-arm-msm@...r.kernel.org,
        linux-bluetooth@...r.kernel.org, linux-hardening@...r.kernel.org,
        linux-hyperv@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-rdma@...r.kernel.org, linux-scsi@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-wireless@...r.kernel.org, linux-xtensa@...ux-xtensa.org,
        llvm@...ts.linux.dev, Loic Poulain <loic.poulain@...aro.org>,
        Louis Peens <louis.peens@...igine.com>,
        Luca Coelho <luciano.coelho@...el.com>,
        Luiz Augusto von Dentz <luiz.dentz@...il.com>,
        Marc Dionne <marc.dionne@...istor.com>,
        Marcel Holtmann <marcel@...tmann.org>,
        Mark Brown <broonie@...nel.org>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Max Filippov <jcmvbkbc@...il.com>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Nathan Chancellor <nathan@...nel.org>, netdev@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nuno Sá <nuno.sa@...log.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Paul Moore <paul@...l-moore.com>,
        Rich Felker <dalias@...ifal.cx>,
        Rob Herring <robh+dt@...nel.org>, selinux@...r.kernel.org,
        "Serge E. Hallyn" <serge@...lyn.com>,
        SHA-cyfmac-dev-list@...ineon.com,
        Simon Horman <simon.horman@...igine.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Stefan Richter <stefanr@...6.in-berlin.de>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Tadeusz Struk <tadeusz.struk@...aro.org>,
        Takashi Iwai <tiwai@...e.com>, Tom Rix <trix@...hat.com>,
        Udipto Goswami <quic_ugoswami@...cinc.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        wcn36xx@...ts.infradead.org, Wei Liu <wei.liu@...nel.org>,
        xen-devel@...ts.xenproject.org,
        Xiu Jianfeng <xiujianfeng@...wei.com>,
        Yang Yingliang <yangyingliang@...wei.com>
Subject: [PATCH 22/32] atags_proc: Use mem_to_flex_dup() with struct buffer

As part of the work to perform bounds checking on all memcpy() uses,
replace the open-coded a deserialization of bytes out of memory into a
trailing flexible array by using a flex_array.h helper to perform the
allocation, bounds checking, and copying.

Cc: Russell King <linux@...linux.org.uk>
Cc: Christian Brauner <brauner@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Muchun Song <songmuchun@...edance.com>
Cc: linux-arm-kernel@...ts.infradead.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 arch/arm/kernel/atags_proc.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/arch/arm/kernel/atags_proc.c b/arch/arm/kernel/atags_proc.c
index 3ec2afe78423..638bbb616daa 100644
--- a/arch/arm/kernel/atags_proc.c
+++ b/arch/arm/kernel/atags_proc.c
@@ -6,8 +6,8 @@
 #include <asm/page.h>
 
 struct buffer {
-	size_t size;
-	char data[];
+	DECLARE_FLEX_ARRAY_ELEMENTS_COUNT(size_t, size);
+	DECLARE_FLEX_ARRAY_ELEMENTS(char, data);
 };
 
 static ssize_t atags_read(struct file *file, char __user *buf,
@@ -38,7 +38,7 @@ static int __init init_atags_procfs(void)
 	 */
 	struct proc_dir_entry *tags_entry;
 	struct tag *tag = (struct tag *)atags_copy;
-	struct buffer *b;
+	struct buffer *b = NULL;
 	size_t size;
 
 	if (tag->hdr.tag != ATAG_CORE) {
@@ -54,13 +54,9 @@ static int __init init_atags_procfs(void)
 
 	WARN_ON(tag->hdr.tag != ATAG_NONE);
 
-	b = kmalloc(sizeof(*b) + size, GFP_KERNEL);
-	if (!b)
+	if (mem_to_flex_dup(&b, atags_copy, size, GFP_KERNEL))
 		goto nomem;
 
-	b->size = size;
-	memcpy(b->data, atags_copy, size);
-
 	tags_entry = proc_create_data("atags", 0400, NULL, &atags_proc_ops, b);
 	if (!tags_entry)
 		goto nomem;
-- 
2.32.0

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