diff options
author | Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> | 2020-07-15 10:51:02 +0900 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2020-08-21 10:52:53 +0200 |
commit | bb4dfb3435708fc15a91a739a295151e34a15686 (patch) | |
tree | b12c11dc24cb4a4d5b5efc7c594f8c1a6a4695c1 /drivers/video | |
parent | bc0ec3258c99115022095b3887a55527ba679bed (diff) |
fbdev: Detect integer underflow at "struct fbcon_ops"->clear_margins.
[ 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@syzkaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: stable <stable@vger.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@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'drivers/video')
-rw-r--r-- | drivers/video/console/bitblit.c | 4 | ||||
-rw-r--r-- | drivers/video/console/fbcon_ccw.c | 4 | ||||
-rw-r--r-- | drivers/video/console/fbcon_cw.c | 4 | ||||
-rw-r--r-- | 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 dbfe4eecf12e..05d1d36a5665 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 5a3cbf6dff4d..34da8bba9273 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 e7ee44db4e98..0b552b3fc22a 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 19e3714abfe8..7f62efe2da52 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; |