From mboxrd@z Thu Jan 1 00:00:00 1970 From: Oleg Nesterov Date: Mon, 24 May 2010 15:14:45 +0000 Subject: Re: [PATCH -mm 1/1] ptrace: PTRACE_GETFDPIC: fix the unsafe usage Message-Id: <20100524151445.GA6393@redhat.com> List-Id: References: <20100522165401.GB19573@redhat.com> <1266280229-18469-1-git-send-email-vapier@gentoo.org> <1274431345-22366-1-git-send-email-vapier@gentoo.org> <20100521162659.GA16193@redhat.com> <20100521183512.4477F40476@magilla.sf.frob.com> <20100522165320.GA19573@redhat.com> <25539.1274711817@redhat.com> In-Reply-To: <25539.1274711817@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: David Howells Cc: Roland McGrath , Andrew Morton , Mike Frysinger , linux-sh@vger.kernel.org, Paul Mundt , uclinux-dist-devel@blackfin.uclinux.org, linux-kernel@vger.kernel.org On 05/24, David Howells wrote: > > Oleg Nesterov wrote: > > > Now that Mike Frysinger unified the FDPIC ptrace code, we can fix > > the unsafe usage of child->mm in ptrace_request(PTRACE_GETFDPIC). > > > > We have the reference to task_struct, and ptrace_check_attach() > > verified the tracee is stopped. But nothing can protect from > > SIGKILL after that, we must not assume child->mm != NULL. > > > > Signed-off-by: Oleg Nesterov > > Acked-by: David Howells > > Does it make sense to move the call to get_task_mm() up to sys_ptrace() since > several ptrace functions use it? The mm pointer could then be handed down the > ptrace hierarchy. You mean, pass it to arch_ptrace() ? grep, grep, grep. I guess I understand you. We have more unsafe code like this in arch/*/kernel/ptrace.c. Of course, it can be fixed without doing get_task_mm() in sys_ptrace(), but perhaps it would be more clean to do what you suggest. Roland, what do you think? Oleg.