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%3Ba=su...
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 stable@vger.kernel.org know about it.
From foo@baz Fri Mar 16 15:11:07 CET 2018
From: "Eric W. Biederman" ebiederm@xmission.com 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" ebiederm@xmission.com
[ 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.
Fixes: 93faccbbfa95 ("fs: Better permission checking for submounts") Fixes: aeaa4a79ff6a ("fs: Call d_automount with the filesystems creds") Acked-by: Ian Kent raven@themaw.net Signed-off-by: "Eric W. Biederman" ebiederm@xmission.com Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/namei.c | 3 --- 1 file changed, 3 deletions(-)
--- a/fs/namei.c +++ b/fs/namei.c @@ -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 ebiederm@xmission.com are
queue-4.15/userns-don-t-fail-follow_automount-based-on-s_user_ns.patch