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Date: Tue,  5 May 2020 17:31:52 +0200
From: Mickaël Salaün <mic@...ikod.net>
To: linux-kernel@...r.kernel.org
Cc: Mickaël Salaün <mic@...ikod.net>,
	Aleksa Sarai <cyphar@...har.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Andy Lutomirski <luto@...nel.org>,
	Christian Heimes <christian@...hon.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Deven Bowers <deven.desai@...ux.microsoft.com>,
	Eric Chiang <ericchiang@...gle.com>,
	Florian Weimer <fweimer@...hat.com>,
	James Morris <jmorris@...ei.org>,
	Jan Kara <jack@...e.cz>,
	Jann Horn <jannh@...gle.com>,
	Jonathan Corbet <corbet@....net>,
	Kees Cook <keescook@...omium.org>,
	Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>,
	Matthew Garrett <mjg59@...gle.com>,
	Matthew Wilcox <willy@...radead.org>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Mickaël Salaün <mickael.salaun@....gouv.fr>,
	Mimi Zohar <zohar@...ux.ibm.com>,
	Philippe Trébuchet <philippe.trebuchet@....gouv.fr>,
	Scott Shell <scottsh@...rosoft.com>,
	Sean Christopherson <sean.j.christopherson@...el.com>,
	Shuah Khan <shuah@...nel.org>,
	Steve Dower <steve.dower@...hon.org>,
	Steve Grubb <sgrubb@...hat.com>,
	Thibaut Sautereau <thibaut.sautereau@....gouv.fr>,
	Vincent Strubel <vincent.strubel@....gouv.fr>,
	kernel-hardening@...ts.openwall.com,
	linux-api@...r.kernel.org,
	linux-integrity@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: [PATCH v5 2/6] fs: Add a MAY_EXECMOUNT flag to infer the noexec mount property

This new MAY_EXECMOUNT flag enables to check if the underlying mount
point of an inode is marked as executable.  This is useful to implement
a security policy taking advantage of the noexec mount option.

This flag is set according to path_noexec(), which checks if a mount
point is mounted with MNT_NOEXEC or if the underlying superblock is
SB_I_NOEXEC.

Signed-off-by: Mickaël Salaün <mic@...ikod.net>
Reviewed-by: Philippe Trébuchet <philippe.trebuchet@....gouv.fr>
Reviewed-by: Thibaut Sautereau <thibaut.sautereau@....gouv.fr>
Cc: Aleksa Sarai <cyphar@...har.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: Kees Cook <keescook@...omium.org>
---
 fs/namei.c         | 2 ++
 include/linux/fs.h | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/fs/namei.c b/fs/namei.c
index a320371899cf..33b6d372e74a 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2849,6 +2849,8 @@ static int may_open(const struct path *path, int acc_mode, int flag)
 		break;
 	}
 
+	/* Pass the mount point executability. */
+	acc_mode |= path_noexec(path) ? 0 : MAY_EXECMOUNT;
 	error = inode_permission(inode, MAY_OPEN | acc_mode);
 	if (error)
 		return error;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 313c934de9ee..79435fca6c3e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -103,6 +103,8 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
 #define MAY_NOT_BLOCK		0x00000080
 /* the inode is opened with O_MAYEXEC */
 #define MAY_OPENEXEC		0x00000100
+/* the mount point is marked as executable */
+#define MAY_EXECMOUNT		0x00000200
 
 /*
  * flags in file.f_mode.  Note that FMODE_READ and FMODE_WRITE must correspond
-- 
2.26.2

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