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23e8b741c8
commit ce684552a266cb1c7cc2f7e623f38567adec6653 upstream. 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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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.