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    Subject[PATCH 5.4 65/85] fork: fix copy_process(CLONE_PARENT) race with the exiting ->real_parent
    Date
    From: Eddy Wu <itseddy0402@gmail.com>

    commit b4e00444cab4c3f3fec876dc0cccc8cbb0d1a948 upstream.

    current->group_leader->exit_signal may change during copy_process() if
    current->real_parent exits.

    Move the assignment inside tasklist_lock to avoid the race.

    Signed-off-by: Eddy Wu <eddy_wu@trendmicro.com>
    Acked-by: Oleg Nesterov <oleg@redhat.com>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    kernel/fork.c | 10 +++++-----
    1 file changed, 5 insertions(+), 5 deletions(-)

    --- a/kernel/fork.c
    +++ b/kernel/fork.c
    @@ -2100,14 +2100,9 @@ static __latent_entropy struct task_stru
    /* ok, now we should be set up.. */
    p->pid = pid_nr(pid);
    if (clone_flags & CLONE_THREAD) {
    - p->exit_signal = -1;
    p->group_leader = current->group_leader;
    p->tgid = current->tgid;
    } else {
    - if (clone_flags & CLONE_PARENT)
    - p->exit_signal = current->group_leader->exit_signal;
    - else
    - p->exit_signal = args->exit_signal;
    p->group_leader = p;
    p->tgid = p->pid;
    }
    @@ -2152,9 +2147,14 @@ static __latent_entropy struct task_stru
    if (clone_flags & (CLONE_PARENT|CLONE_THREAD)) {
    p->real_parent = current->real_parent;
    p->parent_exec_id = current->parent_exec_id;
    + if (clone_flags & CLONE_THREAD)
    + p->exit_signal = -1;
    + else
    + p->exit_signal = current->group_leader->exit_signal;
    } else {
    p->real_parent = current;
    p->parent_exec_id = current->self_exec_id;
    + p->exit_signal = args->exit_signal;
    }

    klp_copy_process(p);

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