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Message-ID: <db4b3346-b9f8-a428-1445-1fcbd8521e1d@samsung.com>
Date: Tue, 14 Jul 2020 09:22:28 +0200
From: Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
To: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Jiri Slaby <jslaby@...e.com>, linux-fbdev@...r.kernel.org,
dri-devel@...ts.freedesktop.org,
Dmitry Vyukov <dvyukov@...gle.com>,
linux-kernel@...r.kernel.org,
George Kennedy <george.kennedy@...cle.com>,
Dan Carpenter <dan.carpenter@...cle.com>
Subject: Re: [PATCH] fbdev: Detect integer underflow at
"struct fbcon_ops"->clear_margins.
[ Please Cc: fbdev Maintainer (happens to be me :) on fbdev patches, thanks. ]
Hi,
On 7/12/20 1:10 PM, Tetsuo Handa wrote:
> I found that
>
> const int fd = open("/dev/fb0", O_ACCMODE);
> struct fb_var_screeninfo var = { };
> ioctl(fd, FBIOGET_VSCREENINFO, &var);
> var.xres = var.yres = 1;
> ioctl(fd, FBIOPUT_VSCREENINFO, &var);
>
> causes general protection fault in bitfill_aligned(), for vc_do_resize()
> updates vc->vc_{cols,rows} only when vc_do_resize() will return 0.
>
> [ 20.102222] BUG: unable to handle page fault for address: ffffb80500d7b000
> [ 20.102225] #PF: supervisor write access in kernel mode
> [ 20.102226] #PF: error_code(0x0002) - not-present page
> [ 20.102227] PGD 13a48c067 P4D 13a48c067 PUD 13a48d067 PMD 132525067 PTE 0
> [ 20.102230] Oops: 0002 [#1] SMP
> [ 20.102232] CPU: 3 PID: 2786 Comm: a.out Not tainted 5.8.0-rc4+ #749
> [ 20.102233] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 02/27/2020
> [ 20.102237] RIP: 0010:bitfill_aligned+0x87/0x120 [cfbfillrect]
> [ 20.102277] Call Trace:
> [ 20.102281] cfb_fillrect+0x159/0x340 [cfbfillrect]
> [ 20.102747] vmw_fb_fillrect+0x12/0x30 [vmwgfx]
> [ 20.102755] bit_clear_margins+0x92/0xf0 [fb]
> [ 20.102760] fbcon_clear_margins+0x4c/0x50 [fb]
> [ 20.102763] fbcon_switch+0x321/0x570 [fb]
> [ 20.102771] redraw_screen+0xe0/0x250
> [ 20.102775] fbcon_modechanged+0x164/0x1b0 [fb]
> [ 20.102779] fbcon_update_vcs+0x15/0x20 [fb]
> [ 20.102781] fb_set_var+0x364/0x3c0 [fb]
> [ 20.102817] do_fb_ioctl+0x2ff/0x3f0 [fb]
> [ 20.103139] fb_ioctl+0x2e/0x40 [fb]
> [ 20.103141] ksys_ioctl+0x86/0xc0
> [ 20.103146] __x64_sys_ioctl+0x15/0x20
> [ 20.103148] do_syscall_64+0x54/0xa0
> [ 20.103151] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> If vc_do_resize() fails (e.g. kzalloc() failure) when var.xres or var.yres
> is going to shrink, bit_clear_margins() hits integer underflow bug due to
> info->var.xres < (vc->vc_cols * cw) or info->var.yres < (vc->vc_rows * ch).
> Unexpectedly large rw or bh will try to overrun the __iomem region and
> causes general protection fault.
>
> This crash is easily reproducible by calling vc_do_resize(vc, 0, 0)
> which the reproducer above will do. Since fbcon_modechanged() is doing
>
> cols = FBCON_SWAP(ops->rotate, info->var.xres, info->var.yres);
> rows = FBCON_SWAP(ops->rotate, info->var.yres, info->var.xres);
> cols /= vc->vc_font.width;
> rows /= vc->vc_font.height;
> vc_resize(vc, cols, rows);
> (...snipped...)
> update_screen(vc);
>
> , var.xres < vc->vc_font.width makes cols = 0 and var.yres < vc->vc_font.height
> makes rows = 0. But vc_do_resize() does not set vc->vc_cols = vc->vc_rows = 0
> due to
>
> new_cols = (cols ? cols : vc->vc_cols);
> new_rows = (lines ? lines : vc->vc_rows);
>
> exception.
>
> Of course, the root problem is that callers of do_vc_resize() are not
> handling vc_do_resize() failures, but it might not be easy to handle
> them under complicated dependency. Therefore, as a band-aid workaround,
> this patch checks integer underflow in "struct fbcon_ops"->clear_margins
> call, assuming that vc->vc_cols * vc->vc_font.width and
> vc->vc_rows * vc->vc_font.heigh do not cause integer overflow.
>
> I hope that we can survive even if info->var.{xres,yres} were increased
> but vc->vc_{cols,rows} were not increased due to kzalloc() failure, for
> the __iomem memory for cfb_fillrect() seems to be allocated upon driver
> load.
>
> By the way, syzbot has several reports which are stalling inside filling
> functions. Although reproducer for [1] is not found yet, it has tried
>
> r0 = openat$fb0(0xffffffffffffff9c, &(0x7f0000000180)='/dev/fb0\x00', 0x0, 0x0)
> ioctl$FBIOPUT_VSCREENINFO(r0, 0x4601, &(0x7f0000000000)={0x0, 0x0, 0x0, 0x500, 0x0, 0x0, 0x4})
>
> which corresponds to
>
> const int fd = open("/dev/fb0", O_ACCMODE);
> struct fb_var_screeninfo var = { };
> var.yres_virtual = 0x500;
> var.bits_per_pixel = 4;
> ioctl(fd, FBIOPUT_VSCREENINFO, &var);
>
> and somehow hit unexpectedly long bit_clear_margins() loops. I don't know
> why syzbot does not hit general protection fault, but it would depend on
> environment because in my VMware environment ioctl(FBIOPUT_VSCREENINFO)
> returns -EINVAL if var.xres == var.yres == 0.
>
> [1] https://syzkaller.appspot.com/bug?id=91ecc3bf32ab1a551c33a39dab7fc0c8cd7b7e16
>
> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
How does this patch relate to:
https://marc.info/?l=linux-fbdev&m=159415024816722&w=2
?
It seems to address the same issue, I've added George and Dan to Cc:.
Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics
> ---
> drivers/video/fbdev/core/bitblit.c | 4 ++--
> drivers/video/fbdev/core/fbcon_ccw.c | 4 ++--
> drivers/video/fbdev/core/fbcon_cw.c | 4 ++--
> drivers/video/fbdev/core/fbcon_ud.c | 4 ++--
> 4 files changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/video/fbdev/core/bitblit.c b/drivers/video/fbdev/core/bitblit.c
> index ca935c09a261..35ebeeccde4d 100644
> --- a/drivers/video/fbdev/core/bitblit.c
> +++ b/drivers/video/fbdev/core/bitblit.c
> @@ -216,7 +216,7 @@ static void bit_clear_margins(struct vc_data *vc, struct fb_info *info,
> region.color = color;
> region.rop = ROP_COPY;
>
> - if (rw && !bottom_only) {
> + if ((int) rw > 0 && !bottom_only) {
> region.dx = info->var.xoffset + rs;
> region.dy = 0;
> region.width = rw;
> @@ -224,7 +224,7 @@ static void bit_clear_margins(struct vc_data *vc, struct fb_info *info,
> info->fbops->fb_fillrect(info, ®ion);
> }
>
> - if (bh) {
> + if ((int) bh > 0) {
> region.dx = info->var.xoffset;
> region.dy = info->var.yoffset + bs;
> region.width = rs;
> diff --git a/drivers/video/fbdev/core/fbcon_ccw.c b/drivers/video/fbdev/core/fbcon_ccw.c
> index dfa9a8aa4509..78f3a5621478 100644
> --- a/drivers/video/fbdev/core/fbcon_ccw.c
> +++ b/drivers/video/fbdev/core/fbcon_ccw.c
> @@ -201,7 +201,7 @@ static void ccw_clear_margins(struct vc_data *vc, struct fb_info *info,
> region.color = color;
> region.rop = ROP_COPY;
>
> - if (rw && !bottom_only) {
> + if ((int) rw > 0 && !bottom_only) {
> region.dx = 0;
> region.dy = info->var.yoffset;
> region.height = rw;
> @@ -209,7 +209,7 @@ static void ccw_clear_margins(struct vc_data *vc, struct fb_info *info,
> info->fbops->fb_fillrect(info, ®ion);
> }
>
> - if (bh) {
> + if ((int) bh > 0) {
> region.dx = info->var.xoffset + bs;
> region.dy = 0;
> region.height = info->var.yres_virtual;
> diff --git a/drivers/video/fbdev/core/fbcon_cw.c b/drivers/video/fbdev/core/fbcon_cw.c
> index ce08251bfd38..fd098ff17574 100644
> --- a/drivers/video/fbdev/core/fbcon_cw.c
> +++ b/drivers/video/fbdev/core/fbcon_cw.c
> @@ -184,7 +184,7 @@ static void cw_clear_margins(struct vc_data *vc, struct fb_info *info,
> region.color = color;
> region.rop = ROP_COPY;
>
> - if (rw && !bottom_only) {
> + if ((int) rw > 0 && !bottom_only) {
> region.dx = 0;
> region.dy = info->var.yoffset + rs;
> region.height = rw;
> @@ -192,7 +192,7 @@ static void cw_clear_margins(struct vc_data *vc, struct fb_info *info,
> info->fbops->fb_fillrect(info, ®ion);
> }
>
> - if (bh) {
> + if ((int) bh > 0) {
> region.dx = info->var.xoffset;
> region.dy = info->var.yoffset;
> region.height = info->var.yres;
> diff --git a/drivers/video/fbdev/core/fbcon_ud.c b/drivers/video/fbdev/core/fbcon_ud.c
> index 1936afc78fec..e165a3fad29a 100644
> --- a/drivers/video/fbdev/core/fbcon_ud.c
> +++ b/drivers/video/fbdev/core/fbcon_ud.c
> @@ -231,7 +231,7 @@ static void ud_clear_margins(struct vc_data *vc, struct fb_info *info,
> region.color = color;
> region.rop = ROP_COPY;
>
> - if (rw && !bottom_only) {
> + if ((int) rw > 0 && !bottom_only) {
> region.dy = 0;
> region.dx = info->var.xoffset;
> region.width = rw;
> @@ -239,7 +239,7 @@ static void ud_clear_margins(struct vc_data *vc, struct fb_info *info,
> info->fbops->fb_fillrect(info, ®ion);
> }
>
> - if (bh) {
> + if ((int) bh > 0) {
> region.dy = info->var.yoffset;
> region.dx = info->var.xoffset;
> region.height = bh;
>
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