Re: [PATCH v3] vsprintf: Prevent crash when dereferencing invalid pointers

Sergey Senozhatsky
2018-03-15T07:58:49Z

On (03/14/18 15:09), Petr Mladek wrote:
[..]
> +static const char *check_pointer_access(const void *ptr)
> +{
> + unsigned char byte;
> +
> + if (!ptr)
> + return "(null)";
> +
> + if (probe_kernel_read(&byte, ptr, 1))
^^^^^
Why one byte? sizeof(ptr)?

[..]
> char *pointer(const char *fmt, char *buf, char *end, void *ptr,
> struct printf_spec spec)
> {
> + static const char data_access_fmt[] = "RrhbMmIiEUVNadCDgGO";
> const int default_width = 2 * sizeof(void *);
> + const char *err_msg = NULL;
> +
> + /* Prevent silent crash when this is called under logbuf_lock. */
> + if (*fmt && strchr(data_access_fmt, *fmt) != NULL)
> + err_msg = check_pointer_access(ptr);

Agree with Rasmus, I think switch() is easier.

-ss