lkml.org 
[lkml]   [2019]   [May]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v2] vt: Fix a missing-check bug in drivers/tty/vt/vt.c
On Tue, 21 May 2019, Gen Zhang wrote:

> On Tue, May 21, 2019 at 12:30:38AM -0400, Nicolas Pitre wrote:
> > Now imagine that MIN_NR_CONSOLES is defined to 10 instead of 1.
> >
> > What happens with allocated memory if the err_vc condition is met on the
> > 5th loop?
> Yes, vc->vc_screenbuf from the last loop is still not freed, right? I
> don't have idea to solve this one. Could please give some advice? Since
> we have to consider the err_vc condition.
>
> > If err_vc_screenbuf condition is encountered on the 5th loop (curcons =
> > 4), what is the value of vc_cons[4].d? Isn't it the same as vc that you
> > just freed?
> >
> >
> > Nicolas
> Thanks for your explaination! You mean a double free situation may
> happen, right? But in vc_allocate() there is also such a kfree(vc) and
> vc_cons[currcons].d = NULL operation. This situation is really confusing
> me.

What you could do is something that looks like:

for (currcons = 0; currcons < MIN_NR_CONSOLES; currcons++) {
vc_cons[currcons].d = vc = kzalloc(...);
if (!vc)
goto fail1;
...
vc->vc_screenbuf = kzalloc(...);
if (!vc->vc_screenbuf)
goto fail2;
...

return 0;

/* free already allocated memory on error */
fail1:
while (curcons > 0) {
curcons--;
kfree(vc_cons[currcons].d->vc_screenbuf);
fail2:
kfree(vc_cons[currcons].d);
vc_cons[currcons].d = NULL;
}
console_unlock();
return -ENOMEM;


Nicolas

\
 
 \ /
  Last update: 2019-05-22 04:44    [W:0.059 / U:7.008 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site