[PATCH v3 2/7] block_dev: Check permissions towards block device inode when mounting

From: Seth Forshee <seth.forshee@canonical.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Serge Hallyn <serge.hallyn@canonical.com>,
	Andy Lutomirski <luto@amacapital.net>,
	linux-kernel@vger.kernel.org, linux-bcache@vger.kernel.org,
	dm-devel@redhat.com, linux-raid@vger.kernel.org,
	linux-mtd@lists.infradead.org, linux-fsdevel@vger.kernel.org,
	linux-security-module@vger.kernel.org, selinux@tycho.nsa.gov,
	Seth Forshee <seth.forshee@canonical.com>
Subject: [PATCH v3 2/7] block_dev: Check permissions towards block device inode when mounting
Date: Tue, 17 Nov 2015 10:39:05 -0600	[thread overview]
Message-ID: <1447778351-118699-3-git-send-email-seth.forshee@canonical.com> (raw)
In-Reply-To: <1447778351-118699-1-git-send-email-seth.forshee@canonical.com>

Unprivileged users should not be able to mount block devices when
they lack sufficient privileges towards the block device inode.
Update blkdev_get_by_path() to validate that the user has the
required access to the inode at the specified path. The check
will be skipped for CAP_SYS_ADMIN, so privileged mounts will
continue working as before.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
---
 fs/block_dev.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index f1f0aa7214a3..54d94cd64577 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1394,9 +1394,14 @@ struct block_device *blkdev_get_by_path(const char *path, fmode_t mode,
 					void *holder)
 {
 	struct block_device *bdev;
+	int perm = 0;
 	int err;
 
-	bdev = lookup_bdev(path, 0);
+	if (mode & FMODE_READ)
+		perm |= MAY_READ;
+	if (mode & FMODE_WRITE)
+		perm |= MAY_WRITE;
+	bdev = lookup_bdev(path, perm);
 	if (IS_ERR(bdev))
 		return bdev;
 
-- 
1.9.1
