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syzbot is reporting general protection fault in do_con_write() [1] caused by vc->vc_screenbuf == ZERO_SIZE_PTR caused by vc->vc_screenbuf_size == 0 caused by vc->vc_cols == vc->vc_rows == vc->vc_size_row == 0 caused by fb_set_var() from ioctl(FBIOPUT_VSCREENINFO) on /dev/fb0 , for gotoxy(vc, 0, 0) from reset_terminal() from vc_init() from vc_allocate() from con_install() from tty_init_dev() from tty_open() on such console causes vc->vc_pos == 0x10000000e due to ((unsigned long) ZERO_SIZE_PTR) + -1U * 0 + (-1U << 1). I don't think that a console with 0 column or 0 row makes sense. And it seems that vc_do_resize() does not intend to allow resizing a console to 0 column or 0 row due to new_cols = (cols ? cols : vc->vc_cols); new_rows = (lines ? lines : vc->vc_rows); exception. Theoretically, cols and rows can be any range as long as 0 < cols * rows * 2 <= KMALLOC_MAX_SIZE is satisfied (e.g. cols == 1048576 && rows == 2 is possible) because of vc->vc_size_row = vc->vc_cols << 1; vc->vc_screenbuf_size = vc->vc_rows * vc->vc_size_row; in visual_init() and kzalloc(vc->vc_screenbuf_size) in vc_allocate(). Since we can detect cols == 0 or rows == 0 via screenbuf_size = 0 in visual_init(), we can reject kzalloc(0). Then, vc_allocate() will return an error, and con_write() will not be called on a console with 0 column or 0 row. We need to make sure that integer overflow in visual_init() won't happen. Since vc_do_resize() restricts cols <= 32767 and rows <= 32767, applying 1 <= cols <= 32767 and 1 <= rows <= 32767 restrictions to vc_allocate() will be practically fine. This patch does not touch con_init(), for returning -EINVAL there does not help when we are not returning -ENOMEM. [1] https://syzkaller.appspot.com/bug?extid=017265e8553724e514e8 Reported-and-tested-by: syzbot <syzbot+017265e8553724e514e8@syzkaller.appspotmail.com> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Cc: stable <stable@vger.kernel.org> Link: https://lore.kernel.org/r/20200712111013.11881-1-penguin-kernel@I-love.SAKURA.ne.jp Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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| .. | ||
| .gitignore | ||
| conmakehash.c | ||
| consolemap.c | ||
| cp437.uni | ||
| defkeymap.c_shipped | ||
| defkeymap.map | ||
| keyboard.c | ||
| Makefile | ||
| selection.c | ||
| vc_screen.c | ||
| vt_ioctl.c | ||
| vt.c | ||