linux-kernel - [PATCH 1/3] fs/exec: don't force writing memory access

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Message-Id: <1478142286-18427-1-git-send-email-jann@thejh.net>
Date:   Thu,  3 Nov 2016 04:04:41 +0100
From:   Jann Horn <jann@...jh.net>
To:     security@...nel.org, Alexander Viro <viro@...iv.linux.org.uk>,
        Paul Moore <paul@...l-moore.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        Eric Paris <eparis@...isplace.org>,
        James Morris <james.l.morris@...cle.com>,
        "Serge E. Hallyn" <serge@...lyn.com>, mchong@...gle.com,
        Andy Lutomirski <luto@...capital.net>,
        Ingo Molnar <mingo@...nel.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Nick Kralevich <nnk@...gle.com>,
        Janis Danisevskis <jdanis@...gle.com>
Cc:     linux-security-module@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/3] fs/exec: don't force writing memory access

This shouldn't change behavior in any way - at this point, there should be
no non-writable mappings, only the initial stack mapping -, but this change
makes it easier to reason about the correctness of the following commits
that place restrictions on forced memory writes.

Signed-off-by: Jann Horn <jann@...jh.net>
Reviewed-by: Janis Danisevskis <jdanis@...roid.com>
---
 fs/exec.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/exec.c b/fs/exec.c
index 4e497b9ee71e..dbc2dd2f0829 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -191,7 +191,7 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
 {
 	struct page *page;
 	int ret;
-	unsigned int gup_flags = FOLL_FORCE;
+	unsigned int gup_flags = 0;
 
 #ifdef CONFIG_STACK_GROWSUP
 	if (write) {
-- 
2.1.4