Messages in this thread | | | Date | Tue, 24 Mar 2020 13:12:36 +0100 | From | Greg KH <> | Subject | Re: UBSAN: Undefined behaviour in drivers/tty/vt/keyboard.c |
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On Mon, Mar 23, 2020 at 04:44:31PM -0400, Kyungtae Kim wrote: > On Mon, Mar 23, 2020 at 07:46:16AM +0100, Greg KH wrote: > > On Sun, Mar 22, 2020 at 11:34:01PM -0400, Kyungtae Kim wrote: > > > We report a bug (in linux-5.5.11) found by FuzzUSB (modified version > > > of syzkaller) > > > > > > Seems the variable "npadch" has a very large value (i.e., 333333333) > > > as a result of multiple executions of the function "k_ascii" (keyboard.c:888) > > > while the variable "base" has 10. > > > So their multiplication at line 888 in "k_ascii" will become > > > larger than the max of type int, causing such an integer overflow. > > > > > > I believe this can be solved by checking for overflow ahead of operations > > > e.g., using check_mul_overflow(). > > > > > > kernel config: https://kt0755.github.io/etc/config_v5.5.11 > > > > Great, can you send a patch for this? > > > > thanks, > > > > greg k-h > > I'm not sure the following works best. > > diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c > index 15d33fa0c925..c1ae9d2e6970 100644 > --- a/drivers/tty/vt/keyboard.c > +++ b/drivers/tty/vt/keyboard.c > @@ -869,6 +869,7 @@ 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; > + int bytes, res; > > if (up_flag) > return; > @@ -884,6 +885,8 @@ 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, &bytes) || > check_add_overflow(bytes, value, &res)) > + return; > else > npadch = npadch * base + value; > }
Does this solve the issue for you? If so, can you fix it up and resend it in a format that I can apply it in?
thanks,
greg k-h
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