LinuxLists.cc - [PATCH] vt: Handle recursion in vc_do

2020-07-29 05:32:22

Subject: [PATCH] vt: Handle recursion in vc_do_resize().

2020-07-29 08:19:38

Subject: Re: [PATCH] vt: Handle recursion in vc_do_resize().

On Wed, Jul 29, 2020 at 8:58 AM Tetsuo Handa
<[email protected]> wrote:
>
> syzbot is reporting OOB read bug in vc_do_resize() [1] caused by memcpy()
> based on outdated old_{rows,row_size} values, for resize_screen() can
> recurse into vc_do_resize() which changes vc->vc_{cols,rows} that outdates
> old_{rows,row_size} values which were read before calling resize_screen().
>
> Minimal fix might be to read vc->vc_{rows,size_row} after resize_screen().
> A different fix might be to forbid recursive vc_do_resize() request.
> I can't tell which fix is the better.
>
> But since I guess that new_cols == vc->vc_cols && new_rows == vc->vc_rows
> check could become true after returning from resize_screen(), and I assume
> that not calling clear_selection() when resize_screen() will return error
> is harmless, let's redo the check by moving resize_screen() earlier.
>
> [1] https://syzkaller.appspot.com/bug?id=c70c88cfd16dcf6e1d3c7f0ab8648b3144b5b25e
>
> Reported-by: syzbot <[email protected]>
> Signed-off-by: Tetsuo Handa <[email protected]>

Ok, I have actual insight on this one here, and I'm pretty sure this
isn't the fix. Looking at the syzkaller splat we have a recursion of
the form

fb_ioctl -> fb_set_var -> fbcon_update_vcs -> fbcon_resize -> fb_set_var

Which isn't supposed to be happening. I've dug around recently in
fbcon code, and this is a fairly common issue: You can update fbcon
state both from fb_ioctl, but also from the vc side. To avoid the
above recursion problems the code is using FBINFO_MISC_USEREVENT, and
should only set that from fb_ioctl entry points. That's all fairly
fragile, so I've done a bit of reworking, e.g.

commit de29ae5c092bd9a5360cfabf174b0f783248d278
Author: Daniel Vetter <[email protected]>
Date: Tue May 28 11:02:56 2019 +0200

fbmem: pull fbcon_fb_blanked out of fb_blank

as an example.

I think doing the same for fb_set_var, i.e. only calling
fbcon_update_vcs for the 3 callers that want it, should fix this
recursion. I think that's the much more robust fix instead of trying
to paper over the fallout of this recursion here and everywhere else.

Can you look into reworking your patch like that?

Cheers, Daniel

> ---
> drivers/tty/vt/vt.c | 24 +++++++++++++++++-------
> 1 file changed, 17 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> index 42d8c67..952a067 100644
> --- a/drivers/tty/vt/vt.c
> +++ b/drivers/tty/vt/vt.c
> @@ -1217,7 +1217,24 @@ static int vc_do_resize(struct tty_struct *tty, struct vc_data *vc,
>
> if (new_cols == vc->vc_cols && new_rows == vc->vc_rows)
> return 0;
> + if (new_screen_size > KMALLOC_MAX_SIZE || !new_screen_size)
> + return -EINVAL;
>
> + /*
> + * Since fbcon_resize() from resize_screen() can recurse into
> + * this function via fb_set_var(), handle recursion now.
> + */
> + err = resize_screen(vc, new_cols, new_rows, user);
> + if (err)
> + return err;
> + /* Reload values in case recursion changed vc->vc_{cols,rows}. */
> + new_cols = (cols ? cols : vc->vc_cols);
> + new_rows = (lines ? lines : vc->vc_rows);
> + new_row_size = new_cols << 1;
> + new_screen_size = new_row_size * new_rows;
> +
> + if (new_cols == vc->vc_cols && new_rows == vc->vc_rows)
> + return 0;
> if (new_screen_size > KMALLOC_MAX_SIZE || !new_screen_size)
> return -EINVAL;
> newscreen = kzalloc(new_screen_size, GFP_USER);
> @@ -1238,13 +1255,6 @@ static int vc_do_resize(struct tty_struct *tty, struct vc_data *vc,
> old_rows = vc->vc_rows;
> old_row_size = vc->vc_size_row;
>
> - err = resize_screen(vc, new_cols, new_rows, user);
> - if (err) {
> - kfree(newscreen);
> - vc_uniscr_free(new_uniscr);
> - return err;
> - }
> -
> vc->vc_rows = new_rows;
> vc->vc_cols = new_cols;
> vc->vc_size_row = new_row_size;
> --
> 1.8.3.1
>
> _______________________________________________
> dri-devel mailing list
> [email protected]
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

2020-07-29 22:48:19

by Tetsuo Handa

[permalink] [raw]

Subject: [PATCH] fbmem: pull fbcon_update_vcs() out of fb_set_var()

syzbot is reporting OOB read bug in vc_do_resize() [1] caused by memcpy()
based on outdated old_{rows,row_size} values, for resize_screen() can
recurse into vc_do_resize() which changes vc->vc_{cols,rows} that outdates
old_{rows,row_size} values which were saved before calling resize_screen().

Daniel Vetter explained that resize_screen() should not recurse into
fbcon_update_vcs() path due to FBINFO_MISC_USEREVENT being still set
when calling resize_screen().

Instead of masking FBINFO_MISC_USEREVENT before calling fbcon_update_vcs(),
we can remove FBINFO_MISC_USEREVENT by calling fbcon_update_vcs() only if
fb_set_var() returned 0. This change assumes that it is harmless to call
fbcon_update_vcs() when fb_set_var() returned 0 without reaching
fb_notifier_call_chain().

[1] https://syzkaller.appspot.com/bug?id=c70c88cfd16dcf6e1d3c7f0ab8648b3144b5b25e

Reported-and-tested-by: syzbot <[email protected]>
Suggested-by: Daniel Vetter <[email protected]>
Signed-off-by: Tetsuo Handa <[email protected]>
---
drivers/video/fbdev/core/fbmem.c | 8 ++------
drivers/video/fbdev/core/fbsysfs.c | 4 ++--
drivers/video/fbdev/ps3fb.c | 4 ++--
include/linux/fb.h | 2 --
4 files changed, 6 insertions(+), 12 deletions(-)

diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index 30e73ec..da7c88f 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -957,7 +957,6 @@ static int fb_check_caps(struct fb_info *info, struct fb_var_screeninfo *var,
int
fb_set_var(struct fb_info *info, struct fb_var_screeninfo *var)
{
- int flags = info->flags;
int ret = 0;
u32 activate;
struct fb_var_screeninfo old_var;
@@ -1052,9 +1051,6 @@ static int fb_check_caps(struct fb_info *info, struct fb_var_screeninfo *var,
event.data = &mode;
fb_notifier_call_chain(FB_EVENT_MODE_CHANGE, &event);

- if (flags & FBINFO_MISC_USEREVENT)
- fbcon_update_vcs(info, activate & FB_ACTIVATE_ALL);
-
return 0;
}
EXPORT_SYMBOL(fb_set_var);
@@ -1105,9 +1101,9 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
return -EFAULT;
console_lock();
lock_fb_info(info);
- info->flags |= FBINFO_MISC_USEREVENT;
ret = fb_set_var(info, &var);
- info->flags &= ~FBINFO_MISC_USEREVENT;
+ if (!ret)
+ fbcon_update_vcs(info, var.activate & FB_ACTIVATE_ALL);
unlock_fb_info(info);
console_unlock();
if (!ret && copy_to_user(argp, &var, sizeof(var)))
diff --git a/drivers/video/fbdev/core/fbsysfs.c b/drivers/video/fbdev/core/fbsysfs.c
index d54c88f..65dae05 100644
--- a/drivers/video/fbdev/core/fbsysfs.c
+++ b/drivers/video/fbdev/core/fbsysfs.c
@@ -91,9 +91,9 @@ static int activate(struct fb_info *fb_info, struct fb_var_screeninfo *var)

var->activate |= FB_ACTIVATE_FORCE;
console_lock();
- fb_info->flags |= FBINFO_MISC_USEREVENT;
err = fb_set_var(fb_info, var);
- fb_info->flags &= ~FBINFO_MISC_USEREVENT;
+ if (!err)
+ fbcon_update_vcs(fb_info, var->activate & FB_ACTIVATE_ALL);
console_unlock();
if (err)
return err;
diff --git a/drivers/video/fbdev/ps3fb.c b/drivers/video/fbdev/ps3fb.c
index 9df78fb..4b4a99f 100644
--- a/drivers/video/fbdev/ps3fb.c
+++ b/drivers/video/fbdev/ps3fb.c
@@ -824,12 +824,12 @@ static int ps3fb_ioctl(struct fb_info *info, unsigned int cmd,
var = info->var;
fb_videomode_to_var(&var, vmode);
console_lock();
- info->flags |= FBINFO_MISC_USEREVENT;
/* Force, in case only special bits changed */
var.activate |= FB_ACTIVATE_FORCE;
par->new_mode_id = val;
retval = fb_set_var(info, &var);
- info->flags &= ~FBINFO_MISC_USEREVENT;
+ if (!retval)
+ fbcon_update_vcs(info, var.activate & FB_ACTIVATE_ALL);
console_unlock();
}
break;
diff --git a/include/linux/fb.h b/include/linux/fb.h
index 3b4b2f0..b11eb02 100644
--- a/include/linux/fb.h
+++ b/include/linux/fb.h
@@ -400,8 +400,6 @@ struct fb_tile_ops {
#define FBINFO_HWACCEL_YPAN 0x2000 /* optional */
#define FBINFO_HWACCEL_YWRAP 0x4000 /* optional */

-#define FBINFO_MISC_USEREVENT 0x10000 /* event request
- from userspace */
#define FBINFO_MISC_TILEBLITTING 0x20000 /* use tile blitting */

/* A driver may set this flag to indicate that it does want a set_par to be
--
1.8.3.1

2020-07-30 10:51:32

by Tetsuo Handa

[permalink] [raw]

Subject: [PATCH v2] fbmem: pull fbcon_update_vcs() out of fb_set_var()

syzbot is reporting OOB read bug in vc_do_resize() [1] caused by memcpy()
based on outdated old_{rows,row_size} values, for resize_screen() can
recurse into vc_do_resize() which changes vc->vc_{cols,rows} that outdates
old_{rows,row_size} values which were saved before calling resize_screen().

Daniel Vetter explained that resize_screen() should not recurse into
fbcon_update_vcs() path due to FBINFO_MISC_USEREVENT being still set
when calling resize_screen().

Instead of masking FBINFO_MISC_USEREVENT before calling fbcon_update_vcs(),
we can remove FBINFO_MISC_USEREVENT by calling fbcon_update_vcs() only if
fb_set_var() returned 0. This change assumes that it is harmless to call
fbcon_update_vcs() when fb_set_var() returned 0 without reaching
fb_notifier_call_chain().

[1] https://syzkaller.appspot.com/bug?id=c70c88cfd16dcf6e1d3c7f0ab8648b3144b5b25e

Reported-and-tested-by: syzbot <[email protected]>
Suggested-by: Daniel Vetter <[email protected]>
Signed-off-by: Tetsuo Handa <[email protected]>
Reported-by: kernel test robot <[email protected]> for missing #include
---
drivers/video/fbdev/core/fbmem.c | 8 ++------
drivers/video/fbdev/core/fbsysfs.c | 4 ++--
drivers/video/fbdev/ps3fb.c | 5 +++--
include/linux/fb.h | 2 --
4 files changed, 7 insertions(+), 12 deletions(-)

diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index 30e73ec..da7c88f 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -957,7 +957,6 @@ static int fb_check_caps(struct fb_info *info, struct fb_var_screeninfo *var,
int
fb_set_var(struct fb_info *info, struct fb_var_screeninfo *var)
{
- int flags = info->flags;
int ret = 0;
u32 activate;
struct fb_var_screeninfo old_var;
@@ -1052,9 +1051,6 @@ static int fb_check_caps(struct fb_info *info, struct fb_var_screeninfo *var,
event.data = &mode;
fb_notifier_call_chain(FB_EVENT_MODE_CHANGE, &event);

- if (flags & FBINFO_MISC_USEREVENT)
- fbcon_update_vcs(info, activate & FB_ACTIVATE_ALL);
-
return 0;
}
EXPORT_SYMBOL(fb_set_var);
@@ -1105,9 +1101,9 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
return -EFAULT;
console_lock();
lock_fb_info(info);
- info->flags |= FBINFO_MISC_USEREVENT;
ret = fb_set_var(info, &var);
- info->flags &= ~FBINFO_MISC_USEREVENT;
+ if (!ret)
+ fbcon_update_vcs(info, var.activate & FB_ACTIVATE_ALL);
unlock_fb_info(info);
console_unlock();
if (!ret && copy_to_user(argp, &var, sizeof(var)))
diff --git a/drivers/video/fbdev/core/fbsysfs.c b/drivers/video/fbdev/core/fbsysfs.c
index d54c88f..65dae05 100644
--- a/drivers/video/fbdev/core/fbsysfs.c
+++ b/drivers/video/fbdev/core/fbsysfs.c
@@ -91,9 +91,9 @@ static int activate(struct fb_info *fb_info, struct fb_var_screeninfo *var)

var->activate |= FB_ACTIVATE_FORCE;
console_lock();
- fb_info->flags |= FBINFO_MISC_USEREVENT;
err = fb_set_var(fb_info, var);
- fb_info->flags &= ~FBINFO_MISC_USEREVENT;
+ if (!err)
+ fbcon_update_vcs(fb_info, var->activate & FB_ACTIVATE_ALL);
console_unlock();
if (err)
return err;
diff --git a/drivers/video/fbdev/ps3fb.c b/drivers/video/fbdev/ps3fb.c
index 9df78fb..203c254 100644
--- a/drivers/video/fbdev/ps3fb.c
+++ b/drivers/video/fbdev/ps3fb.c
@@ -29,6 +29,7 @@
#include <linux/freezer.h>
#include <linux/uaccess.h>
#include <linux/fb.h>
+#include <linux/fbcon.h>
#include <linux/init.h>

#include <asm/cell-regs.h>
@@ -824,12 +825,12 @@ static int ps3fb_ioctl(struct fb_info *info, unsigned int cmd,
var = info->var;
fb_videomode_to_var(&var, vmode);
console_lock();
- info->flags |= FBINFO_MISC_USEREVENT;
/* Force, in case only special bits changed */
var.activate |= FB_ACTIVATE_FORCE;
par->new_mode_id = val;
retval = fb_set_var(info, &var);
- info->flags &= ~FBINFO_MISC_USEREVENT;
+ if (!retval)
+ fbcon_update_vcs(info, var.activate & FB_ACTIVATE_ALL);
console_unlock();
}
break;
diff --git a/include/linux/fb.h b/include/linux/fb.h
index 3b4b2f0..b11eb02 100644
--- a/include/linux/fb.h
+++ b/include/linux/fb.h
@@ -400,8 +400,6 @@ struct fb_tile_ops {
#define FBINFO_HWACCEL_YPAN 0x2000 /* optional */
#define FBINFO_HWACCEL_YWRAP 0x4000 /* optional */

-#define FBINFO_MISC_USEREVENT 0x10000 /* event request
- from userspace */
#define FBINFO_MISC_TILEBLITTING 0x20000 /* use tile blitting */

/* A driver may set this flag to indicate that it does want a set_par to be
--
1.8.3.1

2020-07-30 11:19:11

by Daniel Vetter

[permalink] [raw]

Subject: Re: [PATCH] fbmem: pull fbcon_update_vcs() out of fb_set_var()

On Thu, Jul 30, 2020 at 12:47 AM Tetsuo Handa
<[email protected]> wrote:
>
> syzbot is reporting OOB read bug in vc_do_resize() [1] caused by memcpy()
> based on outdated old_{rows,row_size} values, for resize_screen() can
> recurse into vc_do_resize() which changes vc->vc_{cols,rows} that outdates
> old_{rows,row_size} values which were saved before calling resize_screen().
>
> Daniel Vetter explained that resize_screen() should not recurse into
> fbcon_update_vcs() path due to FBINFO_MISC_USEREVENT being still set
> when calling resize_screen().
>
> Instead of masking FBINFO_MISC_USEREVENT before calling fbcon_update_vcs(),
> we can remove FBINFO_MISC_USEREVENT by calling fbcon_update_vcs() only if
> fb_set_var() returned 0. This change assumes that it is harmless to call
> fbcon_update_vcs() when fb_set_var() returned 0 without reaching
> fb_notifier_call_chain().
>
> [1] https://syzkaller.appspot.com/bug?id=c70c88cfd16dcf6e1d3c7f0ab8648b3144b5b25e
>
> Reported-and-tested-by: syzbot <[email protected]>
> Suggested-by: Daniel Vetter <[email protected]>
> Signed-off-by: Tetsuo Handa <[email protected]>
> ---
> drivers/video/fbdev/core/fbmem.c | 8 ++------
> drivers/video/fbdev/core/fbsysfs.c | 4 ++--
> drivers/video/fbdev/ps3fb.c | 4 ++--
> include/linux/fb.h | 2 --
> 4 files changed, 6 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
> index 30e73ec..da7c88f 100644
> --- a/drivers/video/fbdev/core/fbmem.c
> +++ b/drivers/video/fbdev/core/fbmem.c
> @@ -957,7 +957,6 @@ static int fb_check_caps(struct fb_info *info, struct fb_var_screeninfo *var,
> int
> fb_set_var(struct fb_info *info, struct fb_var_screeninfo *var)
> {
> - int flags = info->flags;
> int ret = 0;
> u32 activate;
> struct fb_var_screeninfo old_var;
> @@ -1052,9 +1051,6 @@ static int fb_check_caps(struct fb_info *info, struct fb_var_screeninfo *var,
> event.data = &mode;
> fb_notifier_call_chain(FB_EVENT_MODE_CHANGE, &event);
>
> - if (flags & FBINFO_MISC_USEREVENT)
> - fbcon_update_vcs(info, activate & FB_ACTIVATE_ALL);
> -
> return 0;
> }
> EXPORT_SYMBOL(fb_set_var);
> @@ -1105,9 +1101,9 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
> return -EFAULT;
> console_lock();
> lock_fb_info(info);
> - info->flags |= FBINFO_MISC_USEREVENT;
> ret = fb_set_var(info, &var);
> - info->flags &= ~FBINFO_MISC_USEREVENT;
> + if (!ret)
> + fbcon_update_vcs(info, var.activate & FB_ACTIVATE_ALL);
> unlock_fb_info(info);
> console_unlock();
> if (!ret && copy_to_user(argp, &var, sizeof(var)))
> diff --git a/drivers/video/fbdev/core/fbsysfs.c b/drivers/video/fbdev/core/fbsysfs.c
> index d54c88f..65dae05 100644
> --- a/drivers/video/fbdev/core/fbsysfs.c
> +++ b/drivers/video/fbdev/core/fbsysfs.c
> @@ -91,9 +91,9 @@ static int activate(struct fb_info *fb_info, struct fb_var_screeninfo *var)
>
> var->activate |= FB_ACTIVATE_FORCE;
> console_lock();
> - fb_info->flags |= FBINFO_MISC_USEREVENT;
> err = fb_set_var(fb_info, var);
> - fb_info->flags &= ~FBINFO_MISC_USEREVENT;
> + if (!err)
> + fbcon_update_vcs(fb_info, var->activate & FB_ACTIVATE_ALL);
> console_unlock();
> if (err)
> return err;
> diff --git a/drivers/video/fbdev/ps3fb.c b/drivers/video/fbdev/ps3fb.c
> index 9df78fb..4b4a99f 100644
> --- a/drivers/video/fbdev/ps3fb.c
> +++ b/drivers/video/fbdev/ps3fb.c
> @@ -824,12 +824,12 @@ static int ps3fb_ioctl(struct fb_info *info, unsigned int cmd,
> var = info->var;
> fb_videomode_to_var(&var, vmode);
> console_lock();
> - info->flags |= FBINFO_MISC_USEREVENT;
> /* Force, in case only special bits changed */
> var.activate |= FB_ACTIVATE_FORCE;
> par->new_mode_id = val;
> retval = fb_set_var(info, &var);
> - info->flags &= ~FBINFO_MISC_USEREVENT;
> + if (!retval)
> + fbcon_update_vcs(info, var.activate & FB_ACTIVATE_ALL);

Patch looks good, except ... does this compile? fbcon_update_vcs is
defined in fbcon.h, and that doesn't seem to be included here ...
Maybe what we want is an fb_set_var_ioctl in fbmem.c so that the fbcon
interaction is a bit better hidden (but that's a bikeshed, feel free
to ignore). Also I have no idea what trickery you need to compile-test
ps3fb, that's why I'm asking :-)
-Daniel

> console_unlock();
> }
> break;
> diff --git a/include/linux/fb.h b/include/linux/fb.h
> index 3b4b2f0..b11eb02 100644
> --- a/include/linux/fb.h
> +++ b/include/linux/fb.h
> @@ -400,8 +400,6 @@ struct fb_tile_ops {
> #define FBINFO_HWACCEL_YPAN 0x2000 /* optional */
> #define FBINFO_HWACCEL_YWRAP 0x4000 /* optional */
>
> -#define FBINFO_MISC_USEREVENT 0x10000 /* event request
> - from userspace */
> #define FBINFO_MISC_TILEBLITTING 0x20000 /* use tile blitting */
>
> /* A driver may set this flag to indicate that it does want a set_par to be
> --
> 1.8.3.1
>
>

--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

2020-07-30 11:28:08

by Tetsuo Handa

[permalink] [raw]

Subject: Re: [PATCH] fbmem: pull fbcon_update_vcs() out of fb_set_var()

On 2020/07/30 20:16, Daniel Vetter wrote:
> Patch looks good, except ... does this compile? fbcon_update_vcs is
> defined in fbcon.h, and that doesn't seem to be included here ...
> Maybe what we want is an fb_set_var_ioctl in fbmem.c so that the fbcon
> interaction is a bit better hidden (but that's a bikeshed, feel free
> to ignore). Also I have no idea what trickery you need to compile-test
> ps3fb, that's why I'm asking :-)

Right. I didn't prepare environment for compiling powerpc kernel.
Kernel test robot found it and I already posted V2 patch as
https://lkml.kernel.org/r/[email protected] .

2020-07-30 11:36:18

by Daniel Vetter

[permalink] [raw]

Subject: Re: [PATCH] fbmem: pull fbcon_update_vcs() out of fb_set_var()

On Thu, Jul 30, 2020 at 1:27 PM Tetsuo Handa
<[email protected]> wrote:
>
> On 2020/07/30 20:16, Daniel Vetter wrote:
> > Patch looks good, except ... does this compile? fbcon_update_vcs is
> > defined in fbcon.h, and that doesn't seem to be included here ...
> > Maybe what we want is an fb_set_var_ioctl in fbmem.c so that the fbcon
> > interaction is a bit better hidden (but that's a bikeshed, feel free
> > to ignore). Also I have no idea what trickery you need to compile-test
> > ps3fb, that's why I'm asking :-)
>
> Right. I didn't prepare environment for compiling powerpc kernel.
> Kernel test robot found it and I already posted V2 patch as
> https://lkml.kernel.org/r/[email protected] .

Excellent. It's still stuck in a queue somewhere and hasn't reached my
inbox, I'll queue it up as soon as I have it.

Thanks, Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

2020-08-04 05:39:27

by Daniel Vetter

[permalink] [raw]

Subject: Re: [PATCH v2] fbmem: pull fbcon_update_vcs() out of fb_set_var()

On Thu, Jul 30, 2020 at 07:47:14PM +0900, Tetsuo Handa wrote:
> syzbot is reporting OOB read bug in vc_do_resize() [1] caused by memcpy()
> based on outdated old_{rows,row_size} values, for resize_screen() can
> recurse into vc_do_resize() which changes vc->vc_{cols,rows} that outdates
> old_{rows,row_size} values which were saved before calling resize_screen().
>
> Daniel Vetter explained that resize_screen() should not recurse into
> fbcon_update_vcs() path due to FBINFO_MISC_USEREVENT being still set
> when calling resize_screen().
>
> Instead of masking FBINFO_MISC_USEREVENT before calling fbcon_update_vcs(),
> we can remove FBINFO_MISC_USEREVENT by calling fbcon_update_vcs() only if
> fb_set_var() returned 0. This change assumes that it is harmless to call
> fbcon_update_vcs() when fb_set_var() returned 0 without reaching
> fb_notifier_call_chain().
>
> [1] https://syzkaller.appspot.com/bug?id=c70c88cfd16dcf6e1d3c7f0ab8648b3144b5b25e
>
> Reported-and-tested-by: syzbot <[email protected]>
> Suggested-by: Daniel Vetter <[email protected]>
> Signed-off-by: Tetsuo Handa <[email protected]>
> Reported-by: kernel test robot <[email protected]> for missing #include

Thanks a lot for your patch, queued up to hopefully still make it for
5.9-rc1.

Cheers, Daniel

> ---
> drivers/video/fbdev/core/fbmem.c | 8 ++------
> drivers/video/fbdev/core/fbsysfs.c | 4 ++--
> drivers/video/fbdev/ps3fb.c | 5 +++--
> include/linux/fb.h | 2 --
> 4 files changed, 7 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
> index 30e73ec..da7c88f 100644
> --- a/drivers/video/fbdev/core/fbmem.c
> +++ b/drivers/video/fbdev/core/fbmem.c
> @@ -957,7 +957,6 @@ static int fb_check_caps(struct fb_info *info, struct fb_var_screeninfo *var,
> int
> fb_set_var(struct fb_info *info, struct fb_var_screeninfo *var)
> {
> - int flags = info->flags;
> int ret = 0;
> u32 activate;
> struct fb_var_screeninfo old_var;
> @@ -1052,9 +1051,6 @@ static int fb_check_caps(struct fb_info *info, struct fb_var_screeninfo *var,
> event.data = &mode;
> fb_notifier_call_chain(FB_EVENT_MODE_CHANGE, &event);
>
> - if (flags & FBINFO_MISC_USEREVENT)
> - fbcon_update_vcs(info, activate & FB_ACTIVATE_ALL);
> -
> return 0;
> }
> EXPORT_SYMBOL(fb_set_var);
> @@ -1105,9 +1101,9 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
> return -EFAULT;
> console_lock();
> lock_fb_info(info);
> - info->flags |= FBINFO_MISC_USEREVENT;
> ret = fb_set_var(info, &var);
> - info->flags &= ~FBINFO_MISC_USEREVENT;
> + if (!ret)
> + fbcon_update_vcs(info, var.activate & FB_ACTIVATE_ALL);
> unlock_fb_info(info);
> console_unlock();
> if (!ret && copy_to_user(argp, &var, sizeof(var)))
> diff --git a/drivers/video/fbdev/core/fbsysfs.c b/drivers/video/fbdev/core/fbsysfs.c
> index d54c88f..65dae05 100644
> --- a/drivers/video/fbdev/core/fbsysfs.c
> +++ b/drivers/video/fbdev/core/fbsysfs.c
> @@ -91,9 +91,9 @@ static int activate(struct fb_info *fb_info, struct fb_var_screeninfo *var)
>
> var->activate |= FB_ACTIVATE_FORCE;
> console_lock();
> - fb_info->flags |= FBINFO_MISC_USEREVENT;
> err = fb_set_var(fb_info, var);
> - fb_info->flags &= ~FBINFO_MISC_USEREVENT;
> + if (!err)
> + fbcon_update_vcs(fb_info, var->activate & FB_ACTIVATE_ALL);
> console_unlock();
> if (err)
> return err;
> diff --git a/drivers/video/fbdev/ps3fb.c b/drivers/video/fbdev/ps3fb.c
> index 9df78fb..203c254 100644
> --- a/drivers/video/fbdev/ps3fb.c
> +++ b/drivers/video/fbdev/ps3fb.c
> @@ -29,6 +29,7 @@
> #include <linux/freezer.h>
> #include <linux/uaccess.h>
> #include <linux/fb.h>
> +#include <linux/fbcon.h>
> #include <linux/init.h>
>
> #include <asm/cell-regs.h>
> @@ -824,12 +825,12 @@ static int ps3fb_ioctl(struct fb_info *info, unsigned int cmd,
> var = info->var;
> fb_videomode_to_var(&var, vmode);
> console_lock();
> - info->flags |= FBINFO_MISC_USEREVENT;
> /* Force, in case only special bits changed */
> var.activate |= FB_ACTIVATE_FORCE;
> par->new_mode_id = val;
> retval = fb_set_var(info, &var);
> - info->flags &= ~FBINFO_MISC_USEREVENT;
> + if (!retval)
> + fbcon_update_vcs(info, var.activate & FB_ACTIVATE_ALL);
> console_unlock();
> }
> break;
> diff --git a/include/linux/fb.h b/include/linux/fb.h
> index 3b4b2f0..b11eb02 100644
> --- a/include/linux/fb.h
> +++ b/include/linux/fb.h
> @@ -400,8 +400,6 @@ struct fb_tile_ops {
> #define FBINFO_HWACCEL_YPAN 0x2000 /* optional */
> #define FBINFO_HWACCEL_YWRAP 0x4000 /* optional */
>
> -#define FBINFO_MISC_USEREVENT 0x10000 /* event request
> - from userspace */
> #define FBINFO_MISC_TILEBLITTING 0x20000 /* use tile blitting */
>
> /* A driver may set this flag to indicate that it does want a set_par to be
> --
> 1.8.3.1
>

--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch