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Message-Id: <20200820091603.311622787@linuxfoundation.org>
Date: Thu, 20 Aug 2020 11:19:52 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org,
Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
Daniel Vetter <daniel.vetter@...ll.ch>,
Sasha Levin <sashal@...nel.org>,
syzbot <syzbot+e5fd3e65515b48c02a30@...kaller.appspotmail.com>
Subject: [PATCH 4.9 019/212] fbdev: Detect integer underflow at "struct fbcon_ops"->clear_margins.
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
[ Upstream commit 033724d6864245a11f8e04c066002e6ad22b3fd0 ]
syzbot is reporting general protection fault in bitfill_aligned() [1]
caused by integer underflow in bit_clear_margins(). The cause of this
problem is when and how do_vc_resize() updates vc->vc_{cols,rows}.
If vc_do_resize() fails (e.g. kzalloc() fails) when var.xres or var.yres
is going to shrink, vc->vc_{cols,rows} will not be updated. This allows
bit_clear_margins() to see 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.
Also, vc_resize(vc, 0, 0) does not set vc->vc_{cols,rows} = 0 due to
new_cols = (cols ? cols : vc->vc_cols);
new_rows = (lines ? lines : vc->vc_rows);
exception. Since cols and lines are calculated as
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);
in fbcon_modechanged(), var.xres < vc->vc_font.width makes cols = 0
and var.yres < vc->vc_font.height makes rows = 0. This means 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);
easily reproduces integer underflow bug explained above.
Of course, callers of vc_resize() are not handling vc_do_resize() failure
is bad. But we can't avoid vc_resize(vc, 0, 0) which returns 0. 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.
[1] https://syzkaller.appspot.com/bug?id=a565882df74fa76f10d3a6fec4be31098dbb37c6
Reported-and-tested-by: syzbot <syzbot+e5fd3e65515b48c02a30@...kaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Acked-by: Daniel Vetter <daniel.vetter@...ll.ch>
Cc: stable <stable@...r.kernel.org>
Link: https://lore.kernel.org/r/20200715015102.3814-1-penguin-kernel@I-love.SAKURA.ne.jp
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
drivers/video/console/bitblit.c | 4 ++--
drivers/video/console/fbcon_ccw.c | 4 ++--
drivers/video/console/fbcon_cw.c | 4 ++--
drivers/video/console/fbcon_ud.c | 4 ++--
4 files changed, 8 insertions(+), 8 deletions(-)
diff --git a/drivers/video/console/bitblit.c b/drivers/video/console/bitblit.c
index dbfe4eecf12e5..05d1d36a56654 100644
--- a/drivers/video/console/bitblit.c
+++ b/drivers/video/console/bitblit.c
@@ -216,7 +216,7 @@ static void bit_clear_margins(struct vc_data *vc, struct fb_info *info,
region.color = 0;
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/console/fbcon_ccw.c b/drivers/video/console/fbcon_ccw.c
index 5a3cbf6dff4d9..34da8bba9273a 100644
--- a/drivers/video/console/fbcon_ccw.c
+++ b/drivers/video/console/fbcon_ccw.c
@@ -201,7 +201,7 @@ static void ccw_clear_margins(struct vc_data *vc, struct fb_info *info,
region.color = 0;
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/console/fbcon_cw.c b/drivers/video/console/fbcon_cw.c
index e7ee44db4e98b..0b552b3fc22ab 100644
--- a/drivers/video/console/fbcon_cw.c
+++ b/drivers/video/console/fbcon_cw.c
@@ -184,7 +184,7 @@ static void cw_clear_margins(struct vc_data *vc, struct fb_info *info,
region.color = 0;
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/console/fbcon_ud.c b/drivers/video/console/fbcon_ud.c
index 19e3714abfe8f..7f62efe2da526 100644
--- a/drivers/video/console/fbcon_ud.c
+++ b/drivers/video/console/fbcon_ud.c
@@ -231,7 +231,7 @@ static void ud_clear_margins(struct vc_data *vc, struct fb_info *info,
region.color = 0;
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;
--
2.25.1
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