From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D53CEC28CF6 for ; Fri, 3 Aug 2018 11:25:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 85C352175D for ; Fri, 3 Aug 2018 11:25:03 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 85C352175D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727419AbeHCNUy (ORCPT ); Fri, 3 Aug 2018 09:20:54 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:38506 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726933AbeHCNUx (ORCPT ); Fri, 3 Aug 2018 09:20:53 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id A6C5540216F7; Fri, 3 Aug 2018 11:24:59 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.34.27.30]) by smtp.corp.redhat.com (Postfix) with SMTP id 39FB42026D65; Fri, 3 Aug 2018 11:24:56 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Fri, 3 Aug 2018 13:24:59 +0200 (CEST) Date: Fri, 3 Aug 2018 13:24:55 +0200 From: Oleg Nesterov To: Ravi Bangoria Cc: srikar@linux.vnet.ibm.com, rostedt@goodmis.org, mhiramat@kernel.org, liu.song.a23@gmail.com, peterz@infradead.org, mingo@redhat.com, acme@kernel.org, alexander.shishkin@linux.intel.com, jolsa@redhat.com, namhyung@kernel.org, linux-kernel@vger.kernel.org, ananth@linux.vnet.ibm.com, alexis.berlemont@gmail.com, naveen.n.rao@linux.vnet.ibm.com, linux-arm-kernel@lists.infradead.org, linux-mips@linux-mips.org, linux@armlinux.org.uk, ralf@linux-mips.org, paul.burton@mips.com Subject: Re: [PATCH v7 3/6] Uprobes: Support SDT markers having reference count (semaphore) Message-ID: <20180803112455.GA13794@redhat.com> References: <20180731035143.11942-1-ravi.bangoria@linux.ibm.com> <20180731035143.11942-4-ravi.bangoria@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180731035143.11942-4-ravi.bangoria@linux.ibm.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.78 on 10.11.54.4 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.5]); Fri, 03 Aug 2018 11:24:59 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.5]); Fri, 03 Aug 2018 11:24:59 +0000 (UTC) for IP:'10.11.54.4' DOMAIN:'int-mx04.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'oleg@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Ravi, I was going to give up and ack this series, but it seems I noticed a bug... On 07/31, Ravi Bangoria wrote: > > +static int delayed_uprobe_add(struct uprobe *uprobe, struct mm_struct *mm) > +{ > + struct delayed_uprobe *du; > + > + if (delayed_uprobe_check(uprobe, mm)) > + return 0; > + > + du = kzalloc(sizeof(*du), GFP_KERNEL); > + if (!du) > + return -ENOMEM; > + > + du->uprobe = uprobe; > + du->mm = mm; I am surprised I didn't notice this before... So du->mm = mm; is fine, mm can't go away, uprobe_clear_state() does delayed_uprobe_remove(NULL,mm). But du->uprobe = uprobe; doesn't look right, uprobe can go away and it can be freed, its memory can be reused. We can't rely on remove_breakpoint(), the application can unmap the probed page/vma. Yes we do not care about the application in this case, say, the next uprobe_mmap() can wrongly increment the counter, we do not care although this can lead to hard-to-debug problems. But, if nothing else, the kernel can crash if the freed memory is unmapped. So I think put_uprobe() should do delayed_uprobe_remove(uprobe, NULL) before kfree() and delayed_uprobe_remove() should be updated to handle the mm==NULL case. Also. delayed_uprobe_add() should check the list and avoid duplicates. Otherwise the trivial for (;;) munmap(mmap(uprobed_file)); will eat the memory until uprobe is unregistered. > +static bool valid_ref_ctr_vma(struct uprobe *uprobe, > + struct vm_area_struct *vma) > +{ > + unsigned long vaddr = offset_to_vaddr(vma, uprobe->ref_ctr_offset); > + > + return uprobe->ref_ctr_offset && > + vma->vm_file && > + file_inode(vma->vm_file) == uprobe->inode && > + vma->vm_flags & VM_WRITE && > + !(vma->vm_flags & VM_SHARED) && vma->vm_flags & (VM_WRITE|VM_SHARED) == VM_WRITE && looks a bit better to me, but I won't insist. > +static int delayed_uprobe_install(struct vm_area_struct *vma) > +{ > + struct list_head *pos, *q; > + struct delayed_uprobe *du; > + unsigned long vaddr; > + int ret = 0, err = 0; > + > + mutex_lock(&delayed_uprobe_lock); > + list_for_each_safe(pos, q, &delayed_uprobe_list) { > + du = list_entry(pos, struct delayed_uprobe, list); > + > + if (!valid_ref_ctr_vma(du->uprobe, vma)) > + continue; > + > + vaddr = offset_to_vaddr(vma, du->uprobe->ref_ctr_offset); > + ret = __update_ref_ctr(vma->vm_mm, vaddr, 1); > + /* Record an error and continue. */ > + err = ret & !err ? ret : err; I try to avoid the cosmetic nits, but I simply can't look at this line ;) if (ret && !err) err = ret; > @@ -1072,7 +1281,14 @@ int uprobe_mmap(struct vm_area_struct *vma) > struct uprobe *uprobe, *u; > struct inode *inode; > > - if (no_uprobe_events() || !valid_vma(vma, true)) > + if (no_uprobe_events()) > + return 0; > + > + if (vma->vm_flags & VM_WRITE && > + test_bit(MMF_HAS_UPROBES, &vma->vm_mm->flags)) > + delayed_uprobe_install(vma); OK, so you also added the VM_WRITE check and I agree. But then I think we should also check VM_SHARED, just like valid_ref_ctr_vma() does? Oleg.