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SubjectRe: [PATCH v5 09/11] vsprintf: Prevent crash when dereferencing invalid pointers
On Wed 2018-04-25 18:10:54, Andy Shevchenko wrote:
> On Wed, 2018-04-25 at 13:12 +0200, Petr Mladek wrote:
> > We already prevent crash when dereferencing some obviously broken
> > pointers. But the handling is not consistent. Sometimes we print
> > "(null)"
> > only for pure NULL pointer, sometimes for pointers in the first
> > page and sometimes also for pointers in the last page (error codes).
> >
> > Note that printk() call this code under logbuf_lock. Any recursive
> > printks are redirected to the printk_safe implementation and the
> > messages
> > are stored into per-CPU buffers. These buffers might be eventually
> > flushed
> > in printk_safe_flush_on_panic() but it is not guaranteed.
>
> > +static const char *check_pointer_access(const void *ptr)
> > +{
> > + char byte;
> > +
> > + if (!ptr)
> > + return "(null)";
> > +
> > + if (probe_kernel_address(ptr, byte))
> > + return "(efault)";
> > +
> > + return NULL;
> > +}
> > +
> > +static bool valid_pointer_access(char **buf, char *end, const void
> > *ptr,
> > + struct printf_spec spec)
> > +{
> > + const char *err_msg;
> > +
> > + err_msg = check_pointer_access(ptr);
> > + if (err_msg) {
> > + *buf = valid_string(*buf, end, err_msg, spec);
> > + return false;
> > + }
> > +
> > + return true;
> > +}
>
> I would preserve similar style of buf pointer handling, i.e.
>
> static char *valid_pointer_access(char **buf, char *end,
> const void *ptr, struct printf_spec spec)
> {
> const char *err_msg;
>
> err_msg = check_pointer_access(ptr);
> if (err_msg)
> return = valid_string(*buf, end, err_msg, spec);
>
> return NULL;
> }

Heh, I actually started with exactly this code. But it caused confusion.
The name suggests that it should return true on success and NULL
is false:

if (!valid_pointer_access())
return err;

Any better naming/code is welcome.

Best Reagrds,
Petr

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