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>

1 files changed, 2 insertions, 2 deletions

diff --git a/fs/hfsplus/posix_acl.c b/fs/hfsplus/posix_acl.c
index ab7ea2506b4d..9b92058a1240 100644
--- a/fs/hfsplus/posix_acl.c
+++ b/fs/hfsplus/posix_acl.c
@@ -65,8 +65,8 @@ int hfsplus_set_posix_acl(struct inode *inode, struct posix_acl *acl,
         case ACL_TYPE_ACCESS:
                 xattr_name = XATTR_NAME_POSIX_ACL_ACCESS;
                 if (acl) {
-                        err = posix_acl_equiv_mode(acl, &inode->i_mode);
-                        if (err < 0)
+                        err = posix_acl_update_mode(inode, &inode->i_mode, &acl);
+                        if (err)
                                 return err;
                 }
                 err = 0;