Strange echo behaviour

Baruch Siach baruch at tkos.co.il
Thu Jan 27 09:39:07 UTC 2011


Hi Peter,

On Thu, Jan 27, 2011 at 10:30:45AM +0100, Peter Korsgaard wrote:
> >>>>> "Baruch" == Baruch Siach <baruch at tkos.co.il> writes:
> 
>  Baruch> Another related problem that I've observed with echo goes as follows:
> 
>  Baruch> ./strace-armv5l sh -c 'echo test > /dev/input/event0'
> 
>  Baruch> shows:
> 
>  Baruch> write(1, "test\n", 5)                   = 16
>  Baruch> write(1, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 2147483647) = -1 EFAULT (Bad address)
> 
> That's a kernel bug. You are supposed to write 16byte long input_event
> structures and not text strings, and evdec.c only checks if it can
> successfully copy_from_user 16 bytes. Depending on malloc
> implementation, the following 11 bytes after the text string are
> probably also within the address space of the process.
> 
> The fix would be something like:

I'm not sure. With this applied I get:

write(1, "test\n", 5)                   = 0
write(1, "test\n", 5)                   = 0
write(1, "test\n", 5)                   = 0
write(1, "test\n", 5)                   = 0
write(1, "test\n", 5)                   = 0

endlessly. Shouldn't write() return some kind of error, say -EINVAL?

baruch

> diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
> index c8471a2..61fa24e 100644
> --- a/drivers/input/evdev.c
> +++ b/drivers/input/evdev.c
> @@ -330,7 +330,7 @@ static ssize_t evdev_write(struct file *file, const char __u
>                 goto out;
>         }
>  
> -       while (retval < count) {
> +       while ((retval + input_event_size()) <= count) {
>  
>                 if (input_event_from_user(buffer + retval, &event)) {
>                         retval = -EFAULT;
> 
> I'll send a patch to the linux-input list.

-- 
                                                     ~. .~   Tk Open Systems
=}------------------------------------------------ooO--U--Ooo------------{=
   - baruch at tkos.co.il - tel: +972.2.679.5364, http://www.tkos.co.il -


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