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 4.9-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:
userns-don-t-fail-follow_automount-based-on-s_user_ns.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 <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Sun Mar 18 16:55:33 CET 2018
From: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
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@xxxxxxxxxxxx>
[ 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@xxxxxxxxxx>
Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/namei.c | 3 ---
1 file changed, 3 deletions(-)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1121,9 +1121,6 @@ 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@xxxxxxxxxxxx are
queue-4.9/userns-don-t-fail-follow_automount-based-on-s_user_ns.patch