Messages in this thread | | | Date | Sun, 9 Jun 2019 00:30:07 +0800 | From | Gen Zhang <> | Subject | Re: [PATCH v3] vt: Fix a missing-check bug in con_init() |
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On Sat, Jun 08, 2019 at 06:22:19PM +0200, 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? I felt like the same when I saw reviewer's advice to write in this way. But I tested, and it did work. > > Ugh, that's beyond ugly. And please provide "real" names for the > labels, "fail1" and "fail2" do not tell anything here.
Sure, I can revise that if needed.
Thanks Gen > > Also, have you actually be able to trigger this? > > thanks, > > greg k-h
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