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Message-ID: <YuZfeJm59UNrw6qE@p100>
Date: Sun, 31 Jul 2022 12:54:48 +0200
From: Helge Deller <deller@....de>
To: Khalid Masum <khalid.masum.92@...il.com>
Cc: Helge Deller <deller@....de>,
syzbot <syzbot+14b0e8f3fd1612e35350@...kaller.appspotmail.com>,
dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Jiri Slaby <jirislaby@...nel.org>
Subject: Re: [syzbot] KASAN: vmalloc-out-of-bounds Write in imageblit (2)
* Khalid Masum <khalid.masum.92@...il.com>:
> On 7/30/22 23:25, Helge Deller wrote:
> > On 7/29/22 08:51, Khalid Masum wrote:
> > > Here is a simplified reproducer for the issue:
> > >
> > > https://gist.githubusercontent.com/Labnann/923d6b9b3a19848fc129637b839b8a55/raw/a68271fcc724569735fe27f80817e561b3ff629a/reproducer.c
> >
> > The reproducer does this:
>
> Thanks for Looking into this. Being to this, so I have some questions.
> > ioctl(3, TIOCLINUX, TIOCL_SETSEL, selection: xs:3 ys:0 xe:0 ye:0 mode:0) = 0
>
> How did you find out the selection values? From strace and man pages I know
> the third argument is an address.
Right. It's a pointer into userspace.
I simply added printk debug code to see what's happening.
I've attached that patch below.
> > -> sets the text selection area
> > ioctl(4, KDFONTOP) with op=0 (con_font_set), charcount=512 width=8 height=32, 0x20000000) = 0
>
> Same here, It would be very helpful if you could tell me how.
See patch below.
> > -> changes the font size.
> >
> > It does not crash with current Linus' head (v5.19-rc8).
>
> I tested in 5.19-rc8 in Qemu x86_64 and it crashed for me.
That's strange, since I tested the same. Maybe I did something wrong.
Anyway, the patches I sent applies to all kernel versions.
> > Kernel v5.16, which was used by this KASAN report, hasn't received backports
> > since months, so I tried stable kernel v5.15.58 instead, and this
> > kernel crashed with the reproducer.
> >
> > The reproducer brings up two issues with current code:
> > 1. The reproducer uses ioctl(TIOCLINUX, TIOCL_SETSEL) and hands over (invalid)
> > zero-values for ys and ye for the starting lines.
> > This is wrong, since the API seems to expect a "1" as the very first line for the selection.
> > This can be easily fixed by adding checks for zero-values and return -EINVAL if found.
> >
> > But this bug isn't critical itself and is not the reason for the kernel crash.
> > Without the checks, the ioctl handler simply wraps the coordinate values and converts them
> > from:
> > input selection: xs:3 ys:0 xe:0 ye:0 mode:0 to the new:
> > vc_selection = xs:2 ys:23 xe:127 ye:23 mode:0
> > which is the current maximum coordinates for the screen.
> >
> > Those higher values now trigger issue #2:
> > After the TIOCL_SETSEL the last line on the screen is now selected. The KDFONTOP ioctl
> > then sets a 8x32 console font, and replaces the former 8x16 console font.
> > With the bigger font the current screen selection is now outside the visible screen
> > and this finally triggeres this backtrace, because vc_do_resize() calls clear_selection()
> > to unhighlight the selection (which starts to render chars outside of the screen):
>
> That makes sense.
>
> > drm_fb_helper_sys_imageblit drivers/gpu/drm/drm_fb_helper.c:794 [inline]
> > drm_fbdev_fb_imageblit+0x15c/0x350 drivers/gpu/drm/drm_fb_helper.c:2288
> > bit_putcs_unaligned drivers/video/fbdev/core/bitblit.c:124 [inline]
> > bit_putcs+0x6e1/0xd20 drivers/video/fbdev/core/bitblit.c:173
> > fbcon_putcs+0x353/0x440 drivers/video/fbdev/core/fbcon.c:1277
> > do_update_region+0x399/0x630 drivers/tty/vt/vt.c:676
> > invert_screen+0x1d4/0x600 drivers/tty/vt/vt.c:800
> > highlight drivers/tty/vt/selection.c:57 [inline]
> > clear_selection drivers/tty/vt/selection.c:84 [inline]
> > clear_selection+0x55/0x70 drivers/tty/vt/selection.c:80
> > vc_do_resize+0xe6e/0x1180 drivers/tty/vt/vt.c:1257
> >
> > IMHO the easiest way to prevent this crash is to simply clear the
> > selection before the various con_font_set() console handlers are called.
> > Otherwise every console driver needs to add checks and verify if the current
> > selection still fits with the selected font, which gets tricky because some
> > of those drivers fiddle with the screen width&height before calling vc_do_resize().
> >
> > I'll follow up to this mail with patches for both issues shortly.
>
> I tested the patches. The crash no longer occurs with the reproducer.
Thanks for testing!
Maybe you want to reply to the patches with a Tested-by: tag?
Below is my debug code.
Helge
diff --git a/drivers/tty/vt/selection.c b/drivers/tty/vt/selection.c
index 58692a9b4097..0167b368a70f 100644
--- a/drivers/tty/vt/selection.c
+++ b/drivers/tty/vt/selection.c
@@ -333,6 +333,7 @@ static int vc_selection(struct vc_data *vc, struct tiocl_selection *v,
v->ys = min_t(u16, v->ys - 1, vc->vc_rows - 1);
v->xe = min_t(u16, v->xe - 1, vc->vc_cols - 1);
v->ye = min_t(u16, v->ye - 1, vc->vc_rows - 1);
+ printk("vc_selection = xs:%u ys:%u xe:%u ye:%u mode:%u\n", v->xs, v->ys, v->xe, v->ye, v->sel_mode);
if (mouse_reporting() && (v->sel_mode & TIOCL_SELMOUSEREPORT)) {
mouse_report(tty, v->sel_mode & TIOCL_SELBUTTONMASK, v->xs,
@@ -357,6 +358,7 @@ int set_selection_kernel(struct tiocl_selection *v, struct tty_struct *tty)
{
int ret;
+ printk("tiocl_selection = xs:%u ys:%u xe:%u ye:%u mode:%u\n", v->xs, v->ys, v->xe, v->ye, v->sel_mode);
mutex_lock(&vc_sel.lock);
console_lock();
ret = vc_selection(vc_cons[fg_console].d, v, tty);
diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 3f09205185a4..a0b4570c959a 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -3194,6 +3194,8 @@ int tioclinux(struct tty_struct *tty, unsigned long arg)
return -EFAULT;
ret = 0;
+ printk("tioclinux: type = %d\n", type); // TIOCL_SETSEL
+
switch (type)
{
case TIOCL_SETSEL:
@@ -4655,6 +4657,8 @@ static int con_font_set(struct vc_data *vc, struct console_font_op *op)
if (IS_ERR(font.data))
return PTR_ERR(font.data);
+ pr_err("con_font_set charcount %d w:%d h:%d\n", op->charcount, op->width, op->height);
+
font.charcount = op->charcount;
font.width = op->width;
font.height = op->height;
@@ -4709,6 +4713,7 @@ static int con_font_default(struct vc_data *vc, struct console_font_op *op)
int con_font_op(struct vc_data *vc, struct console_font_op *op)
{
+ pr_warn("con_font_op op = %d\n", op->op);
switch (op->op) {
case KD_FONT_OP_SET:
return con_font_set(vc, op);
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