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    Subject[PATCH] pidfd: Use new infrastructure to fix deadlocks in execve
    Date
    This changes __pidfd_fget to use the new exec_update_mutex
    instead of cred_guard_mutex.

    This should be safe, as the credentials do not change
    before exec_update_mutex is locked. Therefore whatever
    file access is possible with holding the cred_guard_mutex
    here is also possbile with the exec_update_mutex.

    Signed-off-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
    ---
    kernel/pid.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    This replaces Eric's "[PATCH] pidfd: Stop taking cred_guard_mutex"

    diff --git a/kernel/pid.c b/kernel/pid.c
    index 0f4ecb5..04821f4 100644
    --- a/kernel/pid.c
    +++ b/kernel/pid.c
    @@ -584,7 +584,7 @@ static struct file *__pidfd_fget(struct task_struct *task, int fd)
    struct file *file;
    int ret;

    - ret = mutex_lock_killable(&task->signal->cred_guard_mutex);
    + ret = mutex_lock_killable(&task->signal->exec_update_mutex);
    if (ret)
    return ERR_PTR(ret);

    @@ -593,7 +593,7 @@ static struct file *__pidfd_fget(struct task_struct *task, int fd)
    else
    file = ERR_PTR(-EPERM);

    - mutex_unlock(&task->signal->cred_guard_mutex);
    + mutex_unlock(&task->signal->exec_update_mutex);

    return file ?: ERR_PTR(-EBADF);
    }
    --
    1.9.1
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