vfs: Fix a regression in mounting proc

commit 41301ae78a99ead04ea42672a1ab72c6f44cc81d upstream.

Gao feng <gaofeng@cn.fujitsu.com> reported that commit
e51db73532955dc5eaba4235e62b74b460709d5b
userns: Better restrictions on when proc and sysfs can be mounted
caused a regression on mounting a new instance of proc in a mount
namespace created with user namespace privileges, when binfmt_misc
is mounted on /proc/sys/fs/binfmt_misc.

This is an unintended regression caused by the absolutely bogus empty
directory check in fs_fully_visible.  The check fs_fully_visible replaced
didn't even bother to attempt to verify proc was fully visible and
hiding proc files with any kind of mount is rare.  So for now fix
the userspace regression by allowing directory with nlink == 1
as /proc/sys/fs/binfmt_misc has.

I will have a better patch but it is not stable material, or
last minute kernel material.  So it will have to wait.

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Acked-by: Gao feng <gaofeng@cn.fujitsu.com>
Tested-by: Gao feng <gaofeng@cn.fujitsu.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/namespace.c b/fs/namespace.c
index da5c494834306178dc9efd3b3826d1b7f0e0d17b..84447dbcb650eecba1821d9ef58d1f638f743c9d 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2888,7 +2888,7 @@ bool fs_fully_visible(struct file_system_type *type)
                        struct inode *inode = child->mnt_mountpoint->d_inode;
                        if (!S_ISDIR(inode->i_mode))
                                goto next;
-                       if (inode->i_nlink != 2)
+                       if (inode->i_nlink > 2)
                                goto next;
                }
                visible = true;