This is a note to let you know that I've just added the patch titled

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

to my tty git tree which can be found at git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git in the tty-next branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will also be merged in the next major kernel release during the merge window.

If you have any questions about this process, please let me know.

From 3b0c406124719b625b1aba431659f5cdc24a982c Mon Sep 17 00:00:00 2001

From: Igor Matheus Andrade Torrente igormtorrente@gmail.com Date: Mon, 28 Jun 2021 10:45:09 -0300 Subject: tty: Fix out-of-bound vmalloc access in imageblit

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 --- drivers/tty/vt/vt.c | 21 +++++++++++++++++++-- 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c index ef981d3b7bb4..484eda1958f5 100644 --- a/drivers/tty/vt/vt.c +++ b/drivers/tty/vt/vt.c @@ -1219,8 +1219,25 @@ 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;