Patch "libfs: Modify mount_pseudo_xattr to be clear it is not a userspace mount" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

libfs: Modify mount_pseudo_xattr to be clear it is not a userspace mount

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
libfs-modify-mount_pseudo_xattr-to-be-clear-it-is-not-a-userspace-mount.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: "Eric W. Biederman" <[email protected]>
Date: Wed, 4 Jan 2017 17:37:27 +1300
Subject: libfs: Modify mount_pseudo_xattr to be clear it is not a userspace mount

From: "Eric W. Biederman" <[email protected]>

[ Upstream commit 75422726b0f717d67db3283c2eb5bc14fa2619c5 ]

Add MS_KERNMOUNT to the flags that are passed.
Use sget_userns and force &init_user_ns instead of calling sget so that even if called from a weird context the internal filesystem will be considered to be in the intial user namespace.

Luis Ressel reported that the the failure to pass MS_KERNMOUNT into mount_pseudo broke his in development graphics driver that uses the generic drm infrastructure. I am not certain the deriver was bug free in it's usage of that infrastructure but since mount_pseudo_xattr can never be triggered by userspace it is clearer and less error prone, and less problematic for the code to be explicit.

---
 fs/libfs.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

@@ -245,7 +245,8 @@ struct dentry *mount_pseudo_xattr(struct
 	struct inode *root;
 	struct qstr d_name = QSTR_INIT(name, strlen(name));
 
-	s = sget(fs_type, NULL, set_anon_super, MS_NOUSER, NULL);
+	s = sget_userns(fs_type, NULL, set_anon_super, MS_KERNMOUNT|MS_NOUSER,
+			&init_user_ns, NULL);
 	if (IS_ERR(s))
 		return ERR_CAST(s);
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/libfs-modify-mount_pseudo_xattr-to-be-clear-it-is-not-a-userspace-mount.patch