From: Igor Matheus Andrade Torrente <igormtorrente@xxxxxxxxx> [ 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@xxxxxxxxxxxxxxx> # after 5.15-rc2 is out, give it time to bake Reported-and-tested-by: syzbot+858dc7a2f7ef07c2c219@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Igor Matheus Andrade Torrente <igormtorrente@xxxxxxxxx> Link: https://lore.kernel.org/r/20210628134509.15895-1-igormtorrente@xxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- 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 cb72393f92d3..153d4a88ec9a 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; -- 2.33.0
