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[PATCH 4.4 08/75] bpf: Use mount_nodev not mount_ns to mount the bpf filesystem

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

------------------

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

[ Upstream commit e27f4a942a0ee4b84567a3c6cfa84f273e55cbb7 ]

While reviewing the filesystems that set FS_USERNS_MOUNT I spotted the
bpf filesystem.  Looking at the code I saw a broken usage of mount_ns
with current->nsproxy->mnt_ns. As the code does not acquire a
reference to the mount namespace it can not possibly be correct to
store the mount namespace on the superblock as it does.

Replace mount_ns with mount_nodev so that each mount of the bpf
filesystem returns a distinct instance, and the code is not buggy.

In discussion with Hannes Frederic Sowa it was reported that the use
of mount_ns was an attempt to have one bpf instance per mount
namespace, in an attempt to keep resources that pin resources from
hiding.  That intent simply does not work, the vfs is not built to
allow that kind of behavior.  Which means that the bpf filesystem
really is buggy both semantically and in it's implemenation as it does
not nor can it implement the original intent.

This change is userspace visible, but my experience with similar
filesystems leads me to believe nothing will break with a model of each
mount of the bpf filesystem is distinct from all others.

Fixes: b2197755b263 ("bpf: add support for persistent maps/progs")
Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 kernel/bpf/inode.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/bpf/inode.c
+++ b/kernel/bpf/inode.c
@@ -358,7 +358,7 @@ static int bpf_fill_super(struct super_b
 static struct dentry *bpf_mount(struct file_system_type *type, int flags,
 				const char *dev_name, void *data)
 {
-	return mount_ns(type, flags, current->nsproxy->mnt_ns, bpf_fill_super);
+	return mount_nodev(type, flags, data, bpf_fill_super);
 }
 
 static struct file_system_type bpf_fs_type = {

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[PATCH 4.4 00/75] 4.4.14-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-23 01:30 +0200
  [PATCH 4.4 08/75] bpf: Use mount_nodev not mount_ns to mount the bpf filesystem Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-23 01:30 +0200
  [PATCH 4.4 10/75] uapi glibc compat: fix compilation when !__USE_MISC in glibc Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-23 01:30 +0200
  [PATCH 4.4 14/75] vxlan: Accept user specified MTU value when create new vxlan link Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-23 01:30 +0200
  [PATCH 4.4 18/75] ipv6: Skip XFRM lookup if dst_entry in socket cache is valid Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-23 01:30 +0200
  [PATCH 4.4 13/75] team: dont call netdev_change_features under team->lock Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-23 01:30 +0200
  [PATCH 4.4 03/75] tipc: check nl sock before parsing nested attributes Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-23 01:30 +0200
  [PATCH 4.4 11/75] bpf, inode: disallow userns mounts Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-23 01:30 +0200
  [PATCH 4.4 01/75] scsi_lib: correctly retry failed zero length REQ_TYPE_FS commands Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-23 01:30 +0200
  [PATCH 4.4 12/75] sfc: on MC reset, clear PIO buffer linkage in TXQs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-23 01:30 +0200
  [PATCH 4.4 04/75] netlink: Fix dump skb leak/double free Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-23 01:30 +0200
  [PATCH 4.4 06/75] switchdev: pass pointer to fib_info instead of copy Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-23 01:30 +0200
  [PATCH 4.4 07/75] tuntap: correctly wake up process during uninit Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-23 01:30 +0200
  Re: [PATCH 4.4 00/75] 4.4.14-stable review -rc2 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-23 07:00 +0200

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