Messages in this thread Patch in this message | | | From | Igor Matheus Andrade Torrente <> | Subject | [PATCH RFC] tty: Fix out-of-bound vmalloc access in imageblit | Date | Mon, 31 May 2021 09:47:13 -0300 |
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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 brougth the resize_screen() the beginning of vc_do_resize(), so it will "fix and fill" the fb_var_screeninfo even if the screen does not need any resizing.
Reported-and-tested-by: syzbot+858dc7a2f7ef07c2c219@syzkaller.appspotmail.com Signed-off-by: Igor Matheus Andrade Torrente <igormtorrente@gmail.com> --- drivers/tty/vt/vt.c | 12 ++++-------- 1 file changed, 4 insertions(+), 8 deletions(-)
diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c index fa1548d4f94b..1b90758d8893 100644 --- a/drivers/tty/vt/vt.c +++ b/drivers/tty/vt/vt.c @@ -1219,6 +1219,10 @@ 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; + err = resize_screen(vc, new_cols, new_rows, user); + if (err) + return err; + if (new_cols == vc->vc_cols && new_rows == vc->vc_rows) return 0; @@ -1241,14 +1245,6 @@ static int vc_do_resize(struct tty_struct *tty, struct vc_data *vc, old_rows = vc->vc_rows; old_row_size = vc->vc_size_row; - - err = resize_screen(vc, new_cols, new_rows, user); - if (err) { - kfree(newscreen); - vc_uniscr_free(new_uniscr); - return err; - } - vc->vc_rows = new_rows; vc->vc_cols = new_cols; vc->vc_size_row = new_row_size; -- 2.20.1
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