Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933874Ab1ESSH6 (ORCPT ); Thu, 19 May 2011 14:07:58 -0400 Received: from out2.smtp.messagingengine.com ([66.111.4.26]:33195 "EHLO out2.smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933842Ab1ESSHw (ORCPT ); Thu, 19 May 2011 14:07:52 -0400 X-Sasl-enc: efEvW42wtZTrPJM9IVp9KshLzy2J+OD1hAcyPaIptlkD 1305828471 X-Mailbox-Line: From gregkh@clark.kroah.org Thu May 19 11:05:55 2011 Message-Id: <20110519180555.150198505@clark.kroah.org> User-Agent: quilt/0.48-16.4 Date: Thu, 19 May 2011 11:04:37 -0700 From: Greg KH To: linux-kernel@vger.kernel.org, stable@kernel.org Cc: stable-review@kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Frederic Weisbecker , Ingo Molnar , Peter Zijlstra , Will Deacon , Prasad , Paul Mundt Subject: [09/71] x86, hw_breakpoints: Fix racy access to ptrace breakpoints In-Reply-To: <20110519180626.GA16555@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3000 Lines: 121 2.6.38-stable review patch. If anyone has any objections, please let us know. ------------------ From: Frederic Weisbecker commit 87dc669ba25777b67796d7262c569429e58b1ed4 upstream. While the tracer accesses ptrace breakpoints, the child task may concurrently exit due to a SIGKILL and thus release its breakpoints at the same time. We can then dereference some freed pointers. To fix this, hold a reference on the child breakpoints before manipulating them. Reported-by: Oleg Nesterov Signed-off-by: Frederic Weisbecker Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Will Deacon Cc: Prasad Cc: Paul Mundt Link: http://lkml.kernel.org/r/1302284067-7860-3-git-send-email-fweisbec@gmail.com Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/ptrace.c | 36 ++++++++++++++++++++++++++---------- 1 file changed, 26 insertions(+), 10 deletions(-) --- a/arch/x86/kernel/ptrace.c +++ b/arch/x86/kernel/ptrace.c @@ -608,6 +608,9 @@ static int ptrace_write_dr7(struct task_ unsigned len, type; struct perf_event *bp; + if (ptrace_get_breakpoints(tsk) < 0) + return -ESRCH; + data &= ~DR_CONTROL_RESERVED; old_dr7 = ptrace_get_dr7(thread->ptrace_bps); restore: @@ -655,6 +658,9 @@ restore: } goto restore; } + + ptrace_put_breakpoints(tsk); + return ((orig_ret < 0) ? orig_ret : rc); } @@ -668,10 +674,17 @@ static unsigned long ptrace_get_debugreg if (n < HBP_NUM) { struct perf_event *bp; + + if (ptrace_get_breakpoints(tsk) < 0) + return -ESRCH; + bp = thread->ptrace_bps[n]; if (!bp) - return 0; - val = bp->hw.info.address; + val = 0; + else + val = bp->hw.info.address; + + ptrace_put_breakpoints(tsk); } else if (n == 6) { val = thread->debugreg6; } else if (n == 7) { @@ -686,6 +699,10 @@ static int ptrace_set_breakpoint_addr(st struct perf_event *bp; struct thread_struct *t = &tsk->thread; struct perf_event_attr attr; + int err = 0; + + if (ptrace_get_breakpoints(tsk) < 0) + return -ESRCH; if (!t->ptrace_bps[nr]) { ptrace_breakpoint_init(&attr); @@ -709,24 +726,23 @@ static int ptrace_set_breakpoint_addr(st * writing for the user. And anyway this is the previous * behaviour. */ - if (IS_ERR(bp)) - return PTR_ERR(bp); + if (IS_ERR(bp)) { + err = PTR_ERR(bp); + goto put; + } t->ptrace_bps[nr] = bp; } else { - int err; - bp = t->ptrace_bps[nr]; attr = bp->attr; attr.bp_addr = addr; err = modify_user_hw_breakpoint(bp, &attr); - if (err) - return err; } - - return 0; +put: + ptrace_put_breakpoints(tsk); + return err; } /* -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/