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: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Frederic 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
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@ -608,6 +608,9 @@ static int ptrace_write_dr7(struct task_struct *tsk, unsigned long data)
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unsigned len, type;
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struct perf_event *bp;
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if (ptrace_get_breakpoints(tsk) < 0)
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return -ESRCH;
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data &= ~DR_CONTROL_RESERVED;
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old_dr7 = ptrace_get_dr7(thread->ptrace_bps);
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restore:
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@ -655,6 +658,9 @@ restore:
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}
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goto restore;
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}
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ptrace_put_breakpoints(tsk);
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return ((orig_ret < 0) ? orig_ret : rc);
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}
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@ -668,10 +674,17 @@ static unsigned long ptrace_get_debugreg(struct task_struct *tsk, int n)
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if (n < HBP_NUM) {
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struct perf_event *bp;
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if (ptrace_get_breakpoints(tsk) < 0)
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return -ESRCH;
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bp = thread->ptrace_bps[n];
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if (!bp)
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return 0;
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val = 0;
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else
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val = bp->hw.info.address;
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ptrace_put_breakpoints(tsk);
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} else if (n == 6) {
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val = thread->debugreg6;
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} else if (n == 7) {
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@ -686,6 +699,10 @@ static int ptrace_set_breakpoint_addr(struct task_struct *tsk, int nr,
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struct perf_event *bp;
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struct thread_struct *t = &tsk->thread;
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struct perf_event_attr attr;
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int err = 0;
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if (ptrace_get_breakpoints(tsk) < 0)
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return -ESRCH;
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if (!t->ptrace_bps[nr]) {
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ptrace_breakpoint_init(&attr);
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@ -709,24 +726,23 @@ static int ptrace_set_breakpoint_addr(struct task_struct *tsk, int nr,
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* writing for the user. And anyway this is the previous
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* behaviour.
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*/
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if (IS_ERR(bp))
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return PTR_ERR(bp);
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if (IS_ERR(bp)) {
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err = PTR_ERR(bp);
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goto put;
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}
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t->ptrace_bps[nr] = bp;
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} else {
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int err;
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bp = t->ptrace_bps[nr];
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attr = bp->attr;
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attr.bp_addr = addr;
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err = modify_user_hw_breakpoint(bp, &attr);
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if (err)
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return err;
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}
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return 0;
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put:
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ptrace_put_breakpoints(tsk);
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return err;
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}
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/*
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