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Expressions like u64 = u32 * u32 are unsafe because their products are truncated to u32 even if left hand side is u64. This patch fixes all problems like that one in fbutil. To get right result not only left hand side have to be u64 but it's also necessary to cast at least one of the operands of all leaf operators of right hand side to u64, e.g. u64 = u32 * u32 + u32 * u32 should be u64 = (u64)u32 * u32 + (u64)u32 * u32. For 1-bit bitmaps grub_uint64_t have to be used. It's safe because any combination of values in (grub_uint64_t)u32 * u32 + u32 expression will not overflow grub_uint64_t. Other expressions like ptr + u32 * u32 + u32 * u32 are also vulnerable. They should be ptr + (grub_addr_t)u32 * u32 + (grub_addr_t)u32 * u32. This patch also adds a comment to grub_video_fb_get_video_ptr() which says it's arguments must be valid and no sanity check is performed (like its siblings in grub-core/video/fb/fbutil.c). 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'