Commit 883f7897 authored Jun 28, 2021 by Igor Matheus Andrade Torrente Committed by Greg Kroah-Hartman Oct 06, 2021

tty: Fix out-of-bound vmalloc access in imageblit



[ Upstream commit 3b0c406124719b625b1aba431659f5cdc24a982c ]

This issue happens when a userspace program does an ioctl
FBIOPUT_VSCREENINFO passing the fb_var_screeninfo struct
containing only the fields xres, yres, and bits_per_pixel
with values.

If this struct is the same as the previous ioctl, the
vc_resize() detects it and doesn't call the resize_screen(),
leaving the fb_var_screeninfo incomplete. And this leads to
the updatescrollmode() calculates a wrong value to
fbcon_display->vrows, which makes the real_y() return a
wrong value of y, and that value, eventually, causes
the imageblit to access an out-of-bound address value.

To solve this issue I made the resize_screen() be called
even if the screen does not need any resizing, so it will
"fix and fill" the fb_var_screeninfo independently.

Cc: stable <stable@vger.kernel.org> # after 5.15-rc2 is out, give it time to bake
Reported-and-tested-by:  <syzbot+858dc7a2f7ef07c2c219@syzkaller.appspotmail.com>
Signed-off-by: Igor Matheus Andrade Torrente <igormtorrente@gmail.com>
Link: https://lore.kernel.org/r/20210628134509.15895-1-igormtorrente@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

parent 3a7dc5b4

drivers/tty/vt/vt.c

+19 −2

Original line number	Diff line number	Diff line
		@@ -1215,8 +1215,25 @@ static int vc_do_resize(struct tty_struct tty, struct vc_data vc,
		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_cols == vc->vc_cols && new_rows == vc->vc_rows) {
		/*
		* This function is being called here to cover the case
		* where the userspace calls the FBIOPUT_VSCREENINFO twice,
		* passing the same fb_var_screeninfo containing the fields
		* yres/xres equal to a number non-multiple of vc_font.height
		* and yres_virtual/xres_virtual equal to number lesser than the
		* vc_font.height and yres/xres.
		* In the second call, the struct fb_var_screeninfo isn't
		* being modified by the underlying driver because of the
		* if above, and this causes the fbcon_display->vrows to become
		* negative and it eventually leads to out-of-bound
		* access by the imageblit function.
		* To give the correct values to the struct and to not have
		* to deal with possible errors from the code below, we call
		* the resize_screen here as well.
		*/
		return resize_screen(vc, new_cols, new_rows, user);
		}

		if (new_screen_size > KMALLOC_MAX_SIZE \|\| !new_screen_size)
		return -EINVAL;