linux-kernel - [PATCH 3.12 54/78] mnt: Implicitly add MNT_NODEV on remount when it was implicitly added by mount

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Message-Id: <a4c2b660f35a1f1201cea27d5fbad41482b191fc.1420799385.git.jslaby@suse.cz>
Date:	Fri,  9 Jan 2015 11:32:03 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 54/78] mnt: Implicitly add MNT_NODEV on remount when it was implicitly added by mount

From: "Eric W. Biederman" <ebiederm@...ssion.com>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 3e1866410f11356a9fd869beb3e95983dc79c067 upstream.

Now that remount is properly enforcing the rule that you can't remove
nodev at least sandstorm.io is breaking when performing a remount.

It turns out that there is an easy intuitive solution implicitly
add nodev on remount when nodev was implicitly added on mount.

Tested-by: Cedric Bosdonnat <cbosdonnat@...e.com>
Tested-by: Richard Weinberger <richard@....at>
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 fs/namespace.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index d00750d2f91e..6b42c6d1590e 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1858,7 +1858,13 @@ static int do_remount(struct path *path, int flags, int mnt_flags,
 	}
 	if ((mnt->mnt.mnt_flags & MNT_LOCK_NODEV) &&
 	    !(mnt_flags & MNT_NODEV)) {
-		return -EPERM;
+		/* Was the nodev implicitly added in mount? */
+		if ((mnt->mnt_ns->user_ns != &init_user_ns) &&
+		    !(sb->s_type->fs_flags & FS_USERNS_DEV_MOUNT)) {
+			mnt_flags |= MNT_NODEV;
+		} else {
+			return -EPERM;
+		}
 	}
 	if ((mnt->mnt.mnt_flags & MNT_LOCK_NOSUID) &&
 	    !(mnt_flags & MNT_NOSUID)) {
-- 
2.2.1

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