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    SubjectRe: [PATCH v3] vt: Fix a missing-check bug in con_init()
    On Sat, Jun 08, 2019 at 08:15:46PM -0400, Nicolas Pitre wrote:
    > On Sat, 8 Jun 2019, Greg KH wrote:
    >
    > > On Sun, Jun 09, 2019 at 12:01:38AM +0800, Gen Zhang wrote:
    > > > On Tue, May 28, 2019 at 08:45:29AM +0800, Gen Zhang wrote:
    > > > > In function con_init(), the pointer variable vc_cons[currcons].d, vc and
    > > > > vc->vc_screenbuf is allocated by kzalloc(). And they are used in the
    > > > > following codes. However, kzalloc() returns NULL when fails, and null
    > > > > pointer dereference may happen. And it will cause the kernel to crash.
    > > > > Therefore, we should check the return value and handle the error.
    > > > >
    > > > > Further, since the allcoation is in a loop, we should free all the
    > > > > allocated memory in a loop.
    > > > >
    > > > > Signed-off-by: Gen Zhang <blackgod016574@gmail.com>
    > > > > Reviewed-by: Nicolas Pitre <nico@fluxnic.net>
    > > > > ---
    > > > > diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
    > > > > index fdd12f8..d50f68f 100644
    > > > > --- a/drivers/tty/vt/vt.c
    > > > > +++ b/drivers/tty/vt/vt.c
    > > > > @@ -3350,10 +3350,14 @@ static int __init con_init(void)
    > > > >
    > > > > for (currcons = 0; currcons < MIN_NR_CONSOLES; currcons++) {
    > > > > vc_cons[currcons].d = vc = kzalloc(sizeof(struct vc_data), GFP_NOWAIT);
    > > > > + if (!vc)
    > > > > + goto fail1;
    > > > > INIT_WORK(&vc_cons[currcons].SAK_work, vc_SAK);
    > > > > tty_port_init(&vc->port);
    > > > > visual_init(vc, currcons, 1);
    > > > > vc->vc_screenbuf = kzalloc(vc->vc_screenbuf_size, GFP_NOWAIT);
    > > > > + if (!vc->vc_screenbuf)
    > > > > + goto fail2;
    > > > > vc_init(vc, vc->vc_rows, vc->vc_cols,
    > > > > currcons || !vc->vc_sw->con_save_screen);
    > > > > }
    > > > > @@ -3375,6 +3379,16 @@ static int __init con_init(void)
    > > > > register_console(&vt_console_driver);
    > > > > #endif
    > > > > return 0;
    > > > > +fail1:
    > > > > + while (currcons > 0) {
    > > > > + currcons--;
    > > > > + kfree(vc_cons[currcons].d->vc_screenbuf);
    > > > > +fail2:
    > > > > + kfree(vc_cons[currcons].d);
    > > > > + vc_cons[currcons].d = NULL;
    > > > > + }
    > >
    > > Wait, will that even work? You can jump into the middle of a while
    > > loop?
    >
    > Absolutely.
    >
    > > Ugh, that's beyond ugly.
    >
    > That was me who suggested to do it like that. To me, this is nicer than
    > the proposed alternatives. For an error path that is rather unlikely to
    > happen, I think this is a very concise and eleguant way to do it.
    >
    > > And please provide "real" names for the
    > > labels, "fail1" and "fail2" do not tell anything here.
    >
    > That I agree with.
    >
    >
    > Nicolas
    Thanks for your comments. Then am I supposed to revise the patch and
    send a v4 version?

    Thanks
    Gen

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