Re: [PATCH v2 4/4] proc: avoid ->f_pos overflows inproc_task_readdir() paths

From: Oleg Nesterov
Date: Tue Jun 04 2013 - 13:18:38 EST

On 06/03, Eric W. Biederman wrote:
> Oleg Nesterov <oleg@xxxxxxxxxx> writes:
> > 1. proc_task_readdir() truncates f_pos to long, this can lead
> > to wrong result on 32bit.
> >
> This won't compile on some 32bit architectures like x86-32.
> switch(unsigned long long) requires helpers that the kernel does not
> included. Or at least the kernel has not included because such code
> is a problem. In fact that is the reason Linus put the case to
> unsigned long in there.

Hmm, ee568b25, suprise... I am wondering if the kernel still supports
the compilers which needs __cmpdi2 in this case...

But this doesn't matter. The patch should not blindly revert ee568b25,

> There is another bug in here as well that we may return really crazy
> things in the case of seek simultaneous with readdir.

i_mutex? both vfs_readdir() and default_llseek() take it... Anyway, this
is another issue.

> I think we really need to put f_pos
> in a local variable.

Heh. I swear, this is what I did initially. But I was afraid you will
blame this change as "overcomplicated" ;)

OK, I'll redo/resend this one later.


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