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    Subjectseq_file dangerous assumption?
    I was merging up someone else's driver code from a much older kernel
    to 3.5-rc1 and ran into some issues with corrupted memory. The
    character driver in question was using seq-file.c to handle reads to
    the device. Based on looking around at other drivers, no one else
    does this -- so its probably (well, definitely based on what I found)
    not the right way to do this.

    seq_open seems to make a fairly general assumption:
    (from linux-3.5-rc1 fs/seq_file.c)
    int seq_open(struct file *file, const struct seq_operations *op)
    struct seq_file *p = file->private_data;

    if (!p) {
    p = kmalloc(sizeof(*p), GFP_KERNEL);
    if (!p)
    return -ENOMEM;
    file->private_data = p;
    memset(p, 0, sizeof(*p));

    In other words, if something is in file->private_data, then we must
    have already allocated and put our structure there. In the case of
    this driver, file->private_data was already populated (with a pointer
    to the device structure) -- so the call to seq_open zero'd a portion
    of the device structure and then corrupted it with a seq_file

    So, an obvious solution is, don't use seq_file with a character device
    -- but shouldn't there also be a fingerprint or something in the
    seq_file structure as a sanity check so foolish developers don't trip
    over it and corrupt their kernel memory?


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      Last update: 2012-06-04 22:21    [W:0.023 / U:7.936 seconds]
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