linux-kernel - [PATCH v2 1/2] um: Set secure access mode for temporary file

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Message-Id: <1448805802-12156-2-git-send-email-mic@digikod.net>
Date:	Sun, 29 Nov 2015 15:03:21 +0100
From:	Mickaël Salaün <mic@...ikod.net>
To:	linux-kernel@...r.kernel.org
Cc:	Mickaël Salaün <mic@...ikod.net>,
	Jeff Dike <jdike@...toit.com>,
	Richard Weinberger <richard@....at>,
	Tristan Schmelcher <tschmelcher@...gle.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	user-mode-linux-devel@...ts.sourceforge.net,
	user-mode-linux-user@...ts.sourceforge.net
Subject: [PATCH v2 1/2] um: Set secure access mode for temporary file

Replace the insecure mode 0777 with 0700 for temporary file to prohibit
other users to change the executable mapped code.

An attacker could gain access to the mapped file descriptor from the
temporary file (before it is unlinked) in a read-only mode but it should
not be accessible in write mode to avoid arbitrary code execution.

Signed-off-by: Mickaël Salaün <mic@...ikod.net>
---
 arch/um/os-Linux/mem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/um/os-Linux/mem.c b/arch/um/os-Linux/mem.c
index 897e9ad..798aeb4 100644
--- a/arch/um/os-Linux/mem.c
+++ b/arch/um/os-Linux/mem.c
@@ -142,7 +142,7 @@ static int __init create_tmp_file(unsigned long long len)
 	if (fd < 0)
 		exit(1);
 
-	err = fchmod(fd, 0777);
+	err = fchmod(fd, 0700);
 	if (err < 0) {
 		perror("fchmod");
 		exit(1);
-- 
2.6.2

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