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binfmt_elf: Leave a gap between .bss and brk
Currently the brk starts its randomization immediately after .bss, which means there is a chance that when the random offset is 0, linear overflows from .bss can reach into the brk area. Leave at least a single page gap between .bss and brk (when it has not already been explicitly relocated into the mmap range). Reported-by: <y0un9n132@gmail.com> Closes: https://lore.kernel.org/linux-hardening/CA+2EKTVLvc8hDZc+2Yhwmus=dzOUG5E4gV7ayCbu0MPJTZzWkw@mail.gmail.com/ Link: https://lore.kernel.org/r/20240217062545.1631668-2-keescook@chromium.org Signed-off-by: Kees Cook <keescook@chromium.org>
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@ -1262,6 +1262,9 @@ static int load_elf_binary(struct linux_binprm *bprm)
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if (IS_ENABLED(CONFIG_ARCH_HAS_ELF_RANDOMIZE) &&
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elf_ex->e_type == ET_DYN && !interpreter) {
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mm->brk = mm->start_brk = ELF_ET_DYN_BASE;
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} else {
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/* Otherwise leave a gap between .bss and brk. */
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mm->brk = mm->start_brk = mm->brk + PAGE_SIZE;
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}
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mm->brk = mm->start_brk = arch_randomize_brk(mm);
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