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[PATCH v3 05/21] block_dev: Check permissions towards block device inode when mounting

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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>
Acked-by: Serge Hallyn <serge.hallyn@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 e9b937845bdb..2007040afb7b 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1429,9 +1429,14 @@ 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

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[PATCH v3 00/21] Support fuse mounts in user namespaces Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:40 +0200
  [PATCH v3 17/21] capabilities: Allow privileged user in s_user_ns to set security.* xattrs Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:40 +0200
  [PATCH v3 01/21] fs: fix a posible leak of allocated superblock Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:40 +0200
  [PATCH v3 15/21] fs: Don't remove suid for CAP_FSETID in s_user_ns Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:40 +0200
  [PATCH v3 16/21] fs: Allow superblock owner to access do_remount_sb() Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:50 +0200
  [PATCH v3 05/21] block_dev: Check permissions towards block device inode when mounting Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:50 +0200
  [PATCH v3 04/21] block_dev: Support checking inode permissions in lookup_bdev() Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:50 +0200
  [PATCH v3 12/21] fs: Refuse uid/gid changes which don't map into s_user_ns Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:50 +0200
  [PATCH v3 14/21] fs: Allow superblock owner to change ownership of inodes with unmappable ids Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:50 +0200
    Re: [PATCH v3 14/21] fs: Allow superblock owner to change ownership  of inodes with unmappable ids "Serge E. Hallyn" <serge@hallyn.com> - 2016-04-25 22:40 +0200
      Re: [PATCH v3 14/21] fs: Allow superblock owner to change ownership  of inodes with unmappable ids Seth Forshee <seth.forshee@canonical.com> - 2016-04-26 21:50 +0200
  [PATCH v3 11/21] cred: Reject inodes with invalid ids in set_create_file_as() Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:50 +0200
  [PATCH v3 19/21] fuse: Support fuse filesystems outside of init_user_ns Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:50 +0200
  [PATCH v3 21/21] fuse: Allow user namespace mounts Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:50 +0200
  [PATCH v3 20/21] fuse: Restrict allow_other to the superblock's namespace or a descendant Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:50 +0200
  [PATCH v3 10/21] fs: Check for invalid i_uid in may_follow_link() Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:50 +0200
  [PATCH v3 09/21] Smack: Handle labels consistently in untrusted mounts Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:50 +0200
  [PATCH v3 18/21] fuse: Add support for pid namespaces Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:50 +0200
  [PATCH v3 08/21] userns: Replace in_userns with current_in_userns Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 17:50 +0200
  [PATCH v3 06/21] fs: Treat foreign mounts as nosuid Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 18:00 +0200
  [PATCH v3 07/21] selinux: Add support for unprivileged mounts from user namespaces Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 18:00 +0200
  [PATCH v3 03/21] fs: Allow sysfs and cgroupfs to share super blocks between user namespaces Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 18:00 +0200
    Re: [PATCH v3 03/21] fs: Allow sysfs and cgroupfs to share super  blocks between user namespaces "Serge E. Hallyn" <serge@hallyn.com> - 2016-04-25 21:10 +0200
  [PATCH v3 02/21] fs: Remove check of s_user_ns for existing mounts in fs_fully_visible() Seth Forshee <seth.forshee@canonical.com> - 2016-04-22 18:00 +0200

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