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    SubjectRe: [PATCH -mm 1/1] ptrace: PTRACE_GETFDPIC: fix the unsafe usage of child->mm
    On 05/25, David Howells wrote:
    >
    > Roland McGrath <roland@redhat.com> wrote:
    >
    > > The mm pointer is only used by these uncommon ptrace operations
    >
    > Like PEEKTEXT and POKETEXT?

    They use access_process_vm().

    According to grep, mm is only use to read a couple of members.

    Perhaps can even add the simple helper

    struct mm_xxx {
    unsigned long start_code, end_code, start_data, end_data;
    ... some more ...
    };

    int get_mm_xxx(struct task_struct *tracee, struct mm_xxx *mm_xxx)
    {
    struct mm_struct *mm = get_task_mm(tracee);
    ...
    }

    Except:

    - arch/um/kernel/ptrace.c PTRACE_SWITCH_MM does something
    really strange

    - arch/blackfin/kernel/ptrace.c:is_user_addr_valid()
    needs mmap_sem around find_vma()

    The lockless access to mm->context.sram_list doesn't look
    safe to me.

    If we add get_task_mm() - this protects us against
    destroy_context() only. What is the tracee's sub-thread
    does sys_sram_alloc() or sys_sram_free() in parallel?

    Oleg.



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