linux-kernel - [PATCH v2 1/3] fs/exec: don't force writing memory access

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Date:   Thu, 29 Sep 2016 00:54:39 +0200
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>
Cc:     Nick Kralevich <nnk@...gle.com>,
        Janis Danisevskis <jdanis@...gle.com>,
        linux-security-module@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 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 6fcfb3f..d607da8 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -204,7 +204,7 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
 	 * doing the exec and bprm->mm is the new process's mm.
 	 */
 	ret = get_user_pages_remote(current, bprm->mm, pos, 1, write,
-			1, &page, NULL);
+			0, &page, NULL);
 	if (ret <= 0)
 		return NULL;
 
-- 
2.1.4