From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750788AbWHaUZH (ORCPT ); Thu, 31 Aug 2006 16:25:07 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750810AbWHaUZH (ORCPT ); Thu, 31 Aug 2006 16:25:07 -0400 Received: from mx1.redhat.com ([66.187.233.31]:57480 "EHLO mx1.redhat.com") by vger.kernel.org with ESMTP id S1750788AbWHaUZE (ORCPT ); Thu, 31 Aug 2006 16:25:04 -0400 From: David Howells Subject: [PATCH] NOMMU: Permit ptrace to ignore non-PROT_WRITE VMAs in NOMMU mode Date: Thu, 31 Aug 2006 21:24:29 +0100 To: torvalds@osdl.org, akpm@osdl.org Cc: linux-kernel@vger.kernel.org, uclinux-dev@uclinux.org, dhowells@redhat.com Message-Id: <20060831202429.24083.96888.stgit@warthog.cambridge.redhat.com> Content-Type: text/plain; charset=utf-8; format=fixed Content-Transfer-Encoding: 8bit User-Agent: StGIT/0.10 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org From: David Howells Permit ptrace to modify a section that's non-shared but is marked unwritable, such as is obtained by mapping the text segment of an ELF-FDPIC executable binary with into a binary that's being ptraced[*]. [*] Under NOMMU conditions ptrace causes read-only MAP_PRIVATE mmaps to become totally private copies because if a private mapping was actually shared then the debugging setting breakpoints in it would potentially crash other processes. This is done by using the VM_MAYWRITE flag rather than the VM_WRITE flag when deciding whether to permit a write. Without this patch a debugger can't set breakpoints in the mapped text sections of executables that are mapped read-only private, even if the mmap() syscall has taken a private copy because PT_PTRACED is set. In addition, VM_MAYREAD is used instead of VM_READ for similar reasons. Signed-Off-By: David Howells --- mm/nommu.c | 4 ++-- 1 files changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/nommu.c b/mm/nommu.c index 51e17b9..9d57c2a 100644 --- a/mm/nommu.c +++ b/mm/nommu.c @@ -1234,9 +1234,9 @@ int access_process_vm(struct task_struct len = vma->vm_end - addr; /* only read or write mappings where it is permitted */ - if (write && vma->vm_flags & VM_WRITE) + if (write && vma->vm_flags & VM_MAYWRITE) len -= copy_to_user((void *) addr, buf, len); - else if (!write && vma->vm_flags & VM_READ) + else if (!write && vma->vm_flags & VM_MAYREAD) len -= copy_from_user(buf, (void *) addr, len); else len = 0;