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As a mitigation and hardening measure add sanity checks to grub_font_blit_glyph() and grub_font_blit_glyph_mirror(). This patch makes these two functions do nothing if target blitting area isn't fully contained in target bitmap. Therefore, if complex calculations in caller overflows and malicious coordinates are given, we are still safe because any coordinates which result in out-of-bound-write are rejected. However, this patch only checks for invalid coordinates, and doesn't provide any protection against invalid source glyph or destination glyph, e.g. mismatch between glyph size and buffer size. This hardening measure is designed to mitigate possible overflows in blit_comb(). If overflow occurs, it may return invalid bounding box during dry run and call grub_font_blit_glyph() with malicious coordinates during actual blitting. However, we are still safe because the scratch glyph itself is valid, although its size makes no sense, and any invalid coordinates are rejected. It would be better to call grub_fatal() if illegal parameter is detected. However, doing this may end up in a dangerous recursion because grub_fatal() would print messages to the screen and we are in the progress of drawing characters on the screen. Reported-by: Daniel Axtens <dja@axtens.net> Signed-off-by: Zhang Boyang <zhangboyang.id@gmail.com> Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This is GRUB 2, the second version of the GRand Unified Bootloader. GRUB 2 is rewritten from scratch to make GNU GRUB cleaner, safer, more robust, more powerful, and more portable. See the file NEWS for a description of recent changes to GRUB 2. See the file INSTALL for instructions on how to build and install the GRUB 2 data and program files. See the file MAINTAINERS for information about the GRUB maintainers, etc. If you found a security vulnerability in the GRUB please check the SECURITY file to get more information how to properly report this kind of bugs to the maintainers. Please visit the official web page of GRUB 2, for more information. The URL is <http://www.gnu.org/software/grub/grub.html>. More extensive documentation is available in the Info manual, accessible using 'info grub' after building and installing GRUB 2. There are a number of important user-visible differences from the first version of GRUB, now known as GRUB Legacy. For a summary, please see: info grub Introduction 'Changes from GRUB Legacy'