Messages in this thread | | | Date | Mon, 25 May 2020 09:15:07 +0200 | From | Greg KH <> | Subject | Re: [PATCH v2] vt: keyboard: avoid integer overflow in k_ascii |
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On Sun, May 24, 2020 at 05:08:23PM -0700, Dmitry Torokhov wrote: > On Sat, May 23, 2020 at 11:09:35PM +0000, Kyungtae Kim wrote: > > @@ -884,8 +884,11 @@ static void k_ascii(struct vc_data *vc, unsigned char value, char up_flag) > > > > if (npadch == -1) > > npadch = value; > > + else if (!check_mul_overflow(npadch, base, &new_npadch) && > > + !check_add_overflow(new_npadch, value, &new_npadch)) > > + npadch = new_npadch; > > else > > - npadch = npadch * base + value; > > + return; > > } > > So thinking about it some more, if we use unsigned types, then there is > no issue with overflow UB, and thus maybe we should do something like > this: > > diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c > index 15d33fa0c925..568b2171f335 100644 > --- a/drivers/tty/vt/keyboard.c > +++ b/drivers/tty/vt/keyboard.c > @@ -127,7 +127,11 @@ static DEFINE_SPINLOCK(func_buf_lock); /* guard 'func_buf' and friends */ > static unsigned long key_down[BITS_TO_LONGS(KEY_CNT)]; /* keyboard key bitmap */ > static unsigned char shift_down[NR_SHIFT]; /* shift state counters.. */ > static bool dead_key_next; > -static int npadch = -1; /* -1 or number assembled on pad */ > + > +/* Handles a number being assembled on the number pad */ > +static bool npadch_active;
Much nicer, thanks for that, -1 is not a good thing to try to understand :)
> +static unsigned int npadch_value;
Nicer to just make this a u32 to be explicit about it?
> + > static unsigned int diacr; > static char rep; /* flag telling character repeat */ > > @@ -845,12 +849,12 @@ static void k_shift(struct vc_data *vc, unsigned char value, char up_flag) > shift_state &= ~(1 << value); > > /* kludge */ > - if (up_flag && shift_state != old_state && npadch != -1) { > + if (up_flag && shift_state != old_state && npadch_active) { > if (kbd->kbdmode == VC_UNICODE) > - to_utf8(vc, npadch); > + to_utf8(vc, npadch_value); > else > - put_queue(vc, npadch & 0xff); > - npadch = -1; > + put_queue(vc, npadch_value & 0xff); > + npadch_active = false; > } > } > > @@ -868,7 +872,7 @@ static void k_meta(struct vc_data *vc, unsigned char value, char up_flag) > > static void k_ascii(struct vc_data *vc, unsigned char value, char up_flag) > { > - int base; > + unsigned int base;
u32?
> > if (up_flag) > return; > @@ -882,10 +886,12 @@ static void k_ascii(struct vc_data *vc, unsigned char value, char up_flag) > base = 16; > } > > - if (npadch == -1) > - npadch = value; > - else > - npadch = npadch * base + value; > + if (!npadch_active) { > + npadch_value = 0; > + npadch_active = true; > + } > + > + npadch_value = npadch_value * base + value; > } > > static void k_lock(struct vc_data *vc, unsigned char value, char up_flag) > > > I think if we stop overloading what npadch means, the code becomes more > clear. What do you think?
I think it makes a lot more sense, care to turn this into a "real" patch?
thanks, greg k-h
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