Tue 22 Aug 2017 09:48:01 AM UTC, comment #1:
This is a kernel rather than a setfacl bug. The bug was introduced in v4.9-rc1 by commit 07393101, and fixed around v4.13-rc4 by various commits depending on the filesystem used. The ext4 fix is a3bb2d55. Here are some details:
commit 073931017b49d9458aa351605b43a7e34598caef
Author: Jan Kara <jack@suse.cz>
Date: Mon Sep 19 17:39:09 2016 +0200
posix_acl: Clear SGID bit when setting file permissions
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>
commit a3bb2d5587521eea6dab2d05326abb0afb460abd
Author: Jan Kara <jack@suse.cz>
Date: Sun Jul 30 23:33:01 2017 -0400
ext4: Don't clear SGID when inheriting ACLs
When new directory 'DIR1' is created in a directory 'DIR0' with SGID bit
set, DIR1 is expected to have SGID bit set (and owning group equal to
the owning group of 'DIR0'). However when 'DIR0' also has some default
ACLs that 'DIR1' inherits, setting these ACLs will result in SGID bit on
'DIR1' to get cleared if user is not member of the owning group.
Fix the problem by moving posix_acl_update_mode() out of
__ext4_set_acl() into ext4_set_acl(). That way the function will not be
called when inheriting ACLs which is what we want as it prevents SGID
bit clearing and the mode has been properly set by posix_acl_create()
anyway.
Fixes: 073931017b49d9458aa351605b43a7e34598caef
CC: -unavailable-
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Andreas Gruenbacher <agruenba@redhat.com>
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