Ignore an existing mount if the locked readonly, nodev or atime
attributes are less permissive than the desired attributes
of the new mount.
On success ensure the new mount locks all of the same readonly, nodev and
atime attributes as the old mount.
The nosuid and noexec attributes are not checked here as this change
is destined for stable and enforcing those attributes causes a
regression in lxc and libvirt-lxc where those applications will not
start and there are no known executables on sysfs or proc and no known
way to create exectuables without code modifications
Cc: stable@vger.kernel.org
Fixes: e51db73532955 ("userns: Better restrictions on when proc and sysfs can be mounted")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
-static bool fs_fully_visible(struct file_system_type *fs_type);
+static bool fs_fully_visible(struct file_system_type *fs_type, int *new_mnt_flags);
/*
* create a new mount for userspace and request it to be added into the
/*
* create a new mount for userspace and request it to be added into the
mnt_flags |= MNT_NODEV | MNT_LOCK_NODEV;
}
if (type->fs_flags & FS_USERNS_VISIBLE) {
mnt_flags |= MNT_NODEV | MNT_LOCK_NODEV;
}
if (type->fs_flags & FS_USERNS_VISIBLE) {
- if (!fs_fully_visible(type))
+ if (!fs_fully_visible(type, &mnt_flags))
-static bool fs_fully_visible(struct file_system_type *type)
+static bool fs_fully_visible(struct file_system_type *type, int *new_mnt_flags)
{
struct mnt_namespace *ns = current->nsproxy->mnt_ns;
{
struct mnt_namespace *ns = current->nsproxy->mnt_ns;
+ int new_flags = *new_mnt_flags;
struct mount *mnt;
bool visible = false;
struct mount *mnt;
bool visible = false;
if (mnt->mnt.mnt_root != mnt->mnt.mnt_sb->s_root)
continue;
if (mnt->mnt.mnt_root != mnt->mnt.mnt_sb->s_root)
continue;
+ /* Verify the mount flags are equal to or more permissive
+ * than the proposed new mount.
+ */
+ if ((mnt->mnt.mnt_flags & MNT_LOCK_READONLY) &&
+ !(new_flags & MNT_READONLY))
+ continue;
+ if ((mnt->mnt.mnt_flags & MNT_LOCK_NODEV) &&
+ !(new_flags & MNT_NODEV))
+ continue;
+ if ((mnt->mnt.mnt_flags & MNT_LOCK_ATIME) &&
+ ((mnt->mnt.mnt_flags & MNT_ATIME_MASK) != (new_flags & MNT_ATIME_MASK)))
+ continue;
+
/* This mount is not fully visible if there are any child mounts
* that cover anything except for empty directories.
*/
/* This mount is not fully visible if there are any child mounts
* that cover anything except for empty directories.
*/
if (inode->i_nlink > 2)
goto next;
}
if (inode->i_nlink > 2)
goto next;
}
+ /* Preserve the locked attributes */
+ *new_mnt_flags |= mnt->mnt.mnt_flags & (MNT_LOCK_READONLY | \
+ MNT_LOCK_NODEV | \
+ MNT_LOCK_ATIME);
visible = true;
goto found;
next: ;
visible = true;
goto found;
next: ;