Patch "userns: Don't fail follow_automount based on s_user_ns" has been added to the 4.15-stable tree

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

userns: Don't fail follow_automount based on s_user_ns

to the 4.15-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:
userns-don-t-fail-follow_automount-based-on-s_user_ns.patch
and it can be found in the queue-4.15 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, 29 Nov 2017 17:29:20 -0600
Subject: userns: Don't fail follow_automount based on s_user_ns

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

[ Upstream commit bbc3e471011417598e598707486f5d8814ec9c01 ]

When vfs_submount was added the test to limit automounts from filesystems that with s_user_ns != &init_user_ns accidentially left in follow_automount. The test was never about any security concerns and was always about how do we implement this for filesystems whose s_user_ns != &init_user_ns.

At the moment this check makes no difference as there are no filesystems that both set FS_USERNS_MOUNT and implement d_automount.

Remove this check now while I am thinking about it so there will not be odd booby traps for someone who does want to make this combination work.

vfs_submount still needs improvements to allow this combination to work, and vfs_submount contains a check that presents a warning.

The autofs4 filesystem could be modified to set FS_USERNS_MOUNT and it would need not work on this code path, as userspace performs the mounts.

---
 fs/namei.c |    3 ---
 1 file changed, 3 deletions(-)

@@ -1133,9 +1133,6 @@ static int follow_automount(struct path
 	    path->dentry->d_inode)
 		return -EISDIR;
 
-	if (path->dentry->d_sb->s_user_ns != &init_user_ns)
-		return -EACCES;
-
 	nd->total_link_count++;
 	if (nd->total_link_count >= 40)
 		return -ELOOP;

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

queue-4.15/userns-don-t-fail-follow_automount-based-on-s_user_ns.patch