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    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@gmail.com>
    AuthorDate: Fri, 8 Apr 2011 17:29:36 +0200
    Committer: Frederic Weisbecker <fweisbec@gmail.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@redhat.com>
    Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
    Acked-by: Prasad <prasad@linux.vnet.ibm.com>
    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Will Deacon <will.deacon@arm.com>
    Cc: Paul Mundt <lethal@linux-sh.org>
    Cc: v2.6.33.. <stable@kernel.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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