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Date: Fri, 27 Apr 2018 14:47:21 +0200 From: Petr Mladek <pmladek@...e.com> To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com> Cc: Rasmus Villemoes <linux@...musvillemoes.dk>, Linus Torvalds <torvalds@...ux-foundation.org>, "Tobin C . Harding" <me@...in.cc>, Joe Perches <joe@...ches.com>, Andrew Morton <akpm@...ux-foundation.org>, Michal Hocko <mhocko@...e.cz>, Sergey Senozhatsky <sergey.senozhatsky@...il.com>, Steven Rostedt <rostedt@...dmis.org>, Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>, linux-kernel@...r.kernel.org 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
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