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Commit 87dc669b authored by Frederic Weisbecker's avatar Frederic Weisbecker
Browse files

x86, 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: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Prasad <prasad@linux.vnet.ibm.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: v2.6.33.. <stable@kernel.org>
Link: http://lkml.kernel.org/r/1302284067-7860-3-git-send-email-fweisbec@gmail.com
parent bf26c018

arch/x86/kernel/ptrace.c

+26 −10
Original line number Diff line number Diff line
@@ -608,6 +608,9 @@ static int ptrace_write_dr7(struct task_struct *tsk, unsigned long data) 
	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(struct task_struct *tsk, int n) 


	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 = 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(struct task_struct *tsk, int nr, 
	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(struct task_struct *tsk, int nr, 
		 * 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;

}



/*