Messages in this thread | | | Date | Fri, 27 Apr 2018 14:47:21 +0200 | From | Petr Mladek <> | Subject | Re: [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
| |