On Fri, 2018-03-02 at 13:53 +0100, Petr Mladek wrote: > %p has many modifiers where the pointer is dereferenced. An invalid > pointer might cause kernel to crash silently. > > Note that printk() formats the string 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. > > In general, we should do our best to get useful message from printk(). > All pointers to the first memory page must be invalid. Let's prevent > the dereference and print "(null)" in this case. This is already done > in many other situations, including "%s" format handling and many > page fault handlers. >
With such explanation it makes at least clear for the reader why it's done. Thanks! Would you be okay if I take this one as a first in my series and resubmit the series based on it? > Signed-off-by: Petr Mladek <[email protected]> > --- > lib/vsprintf.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/lib/vsprintf.c b/lib/vsprintf.c > index d7a708f82559..5c2d1f44218a 100644 > --- a/lib/vsprintf.c > +++ b/lib/vsprintf.c > @@ -1849,7 +1849,7 @@ char *pointer(const char *fmt, char *buf, char > *end, void *ptr, > { > const int default_width = 2 * sizeof(void *); > > - if (!ptr && *fmt != 'K' && *fmt != 'x') { > + if ((unsigned long)ptr < PAGE_SIZE && *fmt != 'K' && *fmt != > 'x') { > /* > * Print (null) with the same width as a pointer so > it makes > * tabular output look nice. -- Andy Shevchenko <[email protected]> Intel Finland Oy
