linux-kernel - [tip:perf/urgent] powerpc, hw_breakpoints: Fix racy access to ptrace breakpoints

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Date:	Wed, 4 May 2011 20:29:19 GMT
From:	tip-bot for Frederic Weisbecker <fweisbec@...il.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
	will.deacon@....com, a.p.zijlstra@...llo.nl, lethal@...ux-sh.org,
	fweisbec@...il.com, stable@...nel.org, tglx@...utronix.de,
	oleg@...hat.com, prasad@...ux.vnet.ibm.com, mingo@...e.hu
Subject: [tip:perf/urgent] powerpc, hw_breakpoints: Fix racy access to ptrace breakpoints

Commit-ID:  07fa7a0a8a586c01a8b416358c7012dcb9dc688d
Gitweb:     http://git.kernel.org/tip/07fa7a0a8a586c01a8b416358c7012dcb9dc688d
Author:     Frederic Weisbecker <fweisbec@...il.com>
AuthorDate: Fri, 8 Apr 2011 17:29:36 +0200
Committer:  Frederic Weisbecker <fweisbec@...il.com>
CommitDate: Mon, 25 Apr 2011 17:33:54 +0200

powerpc, hw_breakpoints: Fix racy access to ptrace breakpoints

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 <oleg@...hat.com>
Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
Acked-by: Prasad <prasad@...ux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Will Deacon <will.deacon@....com>
Cc: Paul Mundt <lethal@...ux-sh.org>
Cc: v2.6.33.. <stable@...nel.org>
Link: http://lkml.kernel.org/r/1302284067-7860-4-git-send-email-fweisbec@gmail.com
---
 arch/powerpc/kernel/ptrace.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
index 55613e3..4edeeb3 100644
--- a/arch/powerpc/kernel/ptrace.c
+++ b/arch/powerpc/kernel/ptrace.c
@@ -1591,7 +1591,10 @@ long arch_ptrace(struct task_struct *child, long request,
 	}
 
 	case PTRACE_SET_DEBUGREG:
+		if (ptrace_get_breakpoints(child) < 0)
+			return -ESRCH;
 		ret = ptrace_set_debugreg(child, addr, data);
+		ptrace_put_breakpoints(child);
 		break;
 
 #ifdef CONFIG_PPC64
--
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