Out-of-bounds write in GNU Grub2

A flaw was found in grub2. When performing a symlink lookup from a romfs filesystem, grub's romfs filesystem module uses user-controlled parameters from the filesystem geometry to determine the internal buffer size, however, it improperly checks for integer overflows. A maliciously crafted filesystem may lead some of those buffer size calculations to overflow, causing it to perform a grub_malloc() operation with a smaller size than expected. As a result, the grub_romfs_read_symlink() may cause out-of-bounds writes when the calling grub_disk_read() function. This issue may be leveraged to corrupt grub's internal critical data and can result in arbitrary code execution by-passing secure boot protections.