On Mon, 1 Feb 1999, Matthew Dillon wrote:
> :So, never do stupid things as root; that's always my moto. Well, so I did
> :something stupid as root, but it wasn't inherrently *that* stupid, at
> :least not stupid enough to require a hard boot :). Below is the source
> :...
> :Except I decided to test that feature that overrides the device filename
> :(normally /dev/audit). Instead, I chose /dev/mem. Don't do that (ouch).
> :The machine began to churn -- ok, so the buffer expands as necessary
> :without limit, which is something that will go away once I actually write
> :...
> :swap_pager_getswapspace: failed
> :
> :from the kernel. And needless to say, it loops fairly tightly and we
> :...
>
> Uh. Mmmmmm...... Hmmmmmm :-)
>
> i = read(fd, &size, sizeof(size));
> ... malloc(bufsize * sizeof(char))
> i = read(fd, buf, bufsize);
>
> When you are reading /dev/mem, 'size' can turn out to be anything.
> You are then allocating 'size' bytes ( which could be some insane
> value ). Finally, you try to read() from /dev/mem into the buffer
> the same insane value.
>
> The system is almost certainly trying to kill this process, but it
> can't because the process is stuck in an uninterruptable system read()
> of an insane amount of data.
>
> I don't think there is anything to 'fix' here. The system is making
> the best of a bad situation. Perhaps, though, we could test for signal
> 9 within the insanely huge read() loops and pop out.
I did a signal test inside /dev/urandom (probably yet to be committed, but Bruce
said he was going to.) There's no reason we can't do one here, but we may
have to break read()s of /dev/mem to smaller chunks to allow for this. Maybe
there is a better way to break out of a running system call, and have it
return immediately, but I haven't seen one.
>
> -Matt
>
>
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