Messages in this thread | | | From | Rasmus Villemoes <> | Date | Mon, 5 Mar 2018 16:16:37 +0100 | Subject | Re: [PATCH] vsprintf: Make "null" pointer dereference more robust |
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On 2 March 2018 at 13:53, Petr Mladek <pmladek@suse.com> 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.
Yeah, it's annoying that we can't reliably WARN for bogus vsprintf() uses.
> 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. > > Signed-off-by: Petr Mladek <pmladek@suse.com> > --- > 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') {
ISTM that accidentally passing an ERR_PTR would be just as likely as passing a NULL pointer (or some small offset from one), so if we do this, shouldn't the test also cover IS_ERR values?
Rasmus
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