From a06d3be52bce98746341cfb290203603fd028290 Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@suse.cz>
Date: Mon, 19 Sep 2016 17:39:09 +0200
Subject: [PATCH] posix_acl: Clear SGID bit when setting file permissions

commit 073931017b49d9458aa351605b43a7e34598caef upstream.

When file permissions are modified via chmod(2) and the user is not in
the owning group or capable of CAP_FSETID, the setgid bit is cleared in
inode_change_ok().  Setting a POSIX ACL via setxattr(2) sets the file
permissions as well as the new ACL, but doesn't clear the setgid bit in
a similar way; this allows to bypass the check in chmod(2).  Fix that.

References: CVE-2016-7097
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
[bwh: Backported to 3.2:
 - Drop changes to ceph, f2fs, hfsplus, orangefs
 - Use capable() instead of capable_wrt_inode_uidgid()
 - Update ext3 and generic_acl.c as well
 - In gfs2, jfs, and xfs, take care to avoid leaking the allocated ACL if
   posix_acl_update_mode() determines it's not needed
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
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