netdev - [PATCH 3/8] loop: use ns_capable for some loop operations

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Message-Id: <20200408152151.5780-4-christian.brauner@ubuntu.com>
Date:   Wed,  8 Apr 2020 17:21:46 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Jens Axboe <axboe@...nel.dk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-api@...r.kernel.org
Cc:     Jonathan Corbet <corbet@....net>, Serge Hallyn <serge@...lyn.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>, Tejun Heo <tj@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Saravana Kannan <saravanak@...gle.com>,
        Jan Kara <jack@...e.cz>, David Howells <dhowells@...hat.com>,
        Seth Forshee <seth.forshee@...onical.com>,
        David Rheinsberg <david.rheinsberg@...il.com>,
        Tom Gundersen <teg@...m.no>,
        Christian Kellner <ckellner@...hat.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Stéphane Graber <stgraber@...ntu.com>,
        linux-doc@...r.kernel.org, netdev@...r.kernel.org
Subject: [PATCH 3/8] loop: use ns_capable for some loop operations

The following  LOOP_GET_STATUS, LOOP_SET_STATUS, and LOOP_SET_BLOCK_SIZE
operations are now allowed in non-initial namespaces. Most other
operations were already possible before.

Cc: Jens Axboe <axboe@...nel.dk>
Cc: Seth Forshee <seth.forshee@...onical.com>
Cc: Tom Gundersen <teg@...m.no>
Cc: Tejun Heo <tj@...nel.org>
Cc: Christian Kellner <ckellner@...hat.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: "David S. Miller" <davem@...emloft.net>
Cc: David Rheinsberg <david.rheinsberg@...il.com>
Cc: Dmitry Vyukov <dvyukov@...gle.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>
Signed-off-by: Christian Brauner <christian.brauner@...ntu.com>
---
 drivers/block/loop.c | 29 ++++++++++++++++++++++++-----
 1 file changed, 24 insertions(+), 5 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index a7eda14be639..b1c3436d6e38 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1294,6 +1294,25 @@ void loopfs_remove_locked(struct loop_device *lo)
 	loop_remove(lo);
 	mutex_unlock(&loop_ctl_mutex);
 }
+
+static bool loop_capable(const struct loop_device *lo, int cap)
+{
+	struct super_block *sb;
+	struct user_namespace *ns;
+
+	sb = loopfs_i_sb(lo->lo_loopfs_i);
+	if (sb)
+		ns = sb->s_user_ns;
+	else
+		ns = &init_user_ns;
+
+	return ns_capable(ns, cap);
+}
+#else /* !CONFIG_BLK_DEV_LOOPFS */
+static inline bool loop_capable(const struct loop_device *lo, int cap)
+{
+	return capable(cap);
+}
 #endif /* CONFIG_BLK_DEV_LOOPFS */
 
 static int
@@ -1310,7 +1329,7 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
 		return err;
 	if (lo->lo_encrypt_key_size &&
 	    !uid_eq(lo->lo_key_owner, uid) &&
-	    !capable(CAP_SYS_ADMIN)) {
+	    !loop_capable(lo, CAP_SYS_ADMIN)) {
 		err = -EPERM;
 		goto out_unlock;
 	}
@@ -1441,7 +1460,7 @@ loop_get_status(struct loop_device *lo, struct loop_info64 *info)
 	memcpy(info->lo_crypt_name, lo->lo_crypt_name, LO_NAME_SIZE);
 	info->lo_encrypt_type =
 		lo->lo_encryption ? lo->lo_encryption->number : 0;
-	if (lo->lo_encrypt_key_size && capable(CAP_SYS_ADMIN)) {
+	if (lo->lo_encrypt_key_size && loop_capable(lo, CAP_SYS_ADMIN)) {
 		info->lo_encrypt_key_size = lo->lo_encrypt_key_size;
 		memcpy(info->lo_encrypt_key, lo->lo_encrypt_key,
 		       lo->lo_encrypt_key_size);
@@ -1665,7 +1684,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
 		return loop_clr_fd(lo);
 	case LOOP_SET_STATUS:
 		err = -EPERM;
-		if ((mode & FMODE_WRITE) || capable(CAP_SYS_ADMIN)) {
+		if ((mode & FMODE_WRITE) || loop_capable(lo, CAP_SYS_ADMIN)) {
 			err = loop_set_status_old(lo,
 					(struct loop_info __user *)arg);
 		}
@@ -1674,7 +1693,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
 		return loop_get_status_old(lo, (struct loop_info __user *) arg);
 	case LOOP_SET_STATUS64:
 		err = -EPERM;
-		if ((mode & FMODE_WRITE) || capable(CAP_SYS_ADMIN)) {
+		if ((mode & FMODE_WRITE) || loop_capable(lo, CAP_SYS_ADMIN)) {
 			err = loop_set_status64(lo,
 					(struct loop_info64 __user *) arg);
 		}
@@ -1684,7 +1703,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
 	case LOOP_SET_CAPACITY:
 	case LOOP_SET_DIRECT_IO:
 	case LOOP_SET_BLOCK_SIZE:
-		if (!(mode & FMODE_WRITE) && !capable(CAP_SYS_ADMIN))
+		if (!(mode & FMODE_WRITE) && !loop_capable(lo, CAP_SYS_ADMIN))
 			return -EPERM;
 		/* Fall through */
 	default:
-- 
2.26.0