Messages in this thread | | | Date | Fri, 10 Jun 2022 16:30:10 +0200 | From | Greg KH <> | Subject | Re: [PATCH 1/2] char: lp: ensure that index has not exceeded LP_NO |
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On Fri, Jun 10, 2022 at 07:12:02PM +0530, Shreenidhi Shedi wrote: > On 10/06/22 6:58 pm, Greg KH wrote: > > On Fri, Jun 03, 2022 at 06:30:39PM +0530, Shreenidhi Shedi wrote: > >> From: Shreenidhi Shedi <sshedi@vmware.com> > >> > >> After finishing the loop, index value can be equal to LP_NO and lp_table > >> array is of size LP_NO, so this can end up in accessing an out of bound > >> address in lp_register function. > >> > >> Signed-off-by: Shreenidhi Shedi <sshedi@vmware.com> > >> --- > >> drivers/char/lp.c | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/drivers/char/lp.c b/drivers/char/lp.c > >> index 0e22e3b0a..d474d02b6 100644 > >> --- a/drivers/char/lp.c > >> +++ b/drivers/char/lp.c > >> @@ -972,7 +972,7 @@ static void lp_attach(struct parport *port) > >> if (port_num[i] == -1) > >> break; > >> > >> - if (!lp_register(i, port)) > >> + if (i < LP_NO && !lp_register(i, port)) > >> lp_count++; > > > > How can this ever be needed? Look at the check further up for the check > > of lp_count which prevents this from every going too large. > > > > So how can an address be accessed out of bound here? > > > > thanks, > > > > greg k-h > > Thanks for the review. Assume lp_count is less than LP_NO now and we enter the for loop > and for some reason for loop exits after i reaching the value LP_NO
Wait, how can that happen? That's what I am saying, the loop will never reach that value from what I can tell.
Yes, this whole thing should be moved to something more sane like an idr structure, but as-is, it seems correct to me.
Have you tested the code with that many devices to see if it really can overflow?
thanks,
greg k-h
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