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binfmt_elf: Leave a gap between .bss and brk

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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>
This commit is contained in:
Kees Cook 2024-02-16 22:25:44 -08:00
parent a9c3475dd6
commit 2a5eb99955
1 changed files with 3 additions and 0 deletions
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3
fs/binfmt_elf.c
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@ -1262,6 +1262,9 @@ static int load_elf_binary(struct linux_binprm *bprm)
if (IS_ENABLED(CONFIG_ARCH_HAS_ELF_RANDOMIZE) &&
elf_ex->e_type == ET_DYN && !interpreter) {
mm->brk = mm->start_brk = ELF_ET_DYN_BASE;
} else {
/* Otherwise leave a gap between .bss and brk. */
mm->brk = mm->start_brk = mm->brk + PAGE_SIZE;
}
mm->brk = mm->start_brk = arch_randomize_brk(mm);