From: Kees Cook keescook@chromium.org
[ Upstream commit 2a5eb9995528441447d33838727f6ec1caf08139 ]
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=dzOUG5E4gV7... Link: https://lore.kernel.org/r/20240217062545.1631668-2-keescook@chromium.org Signed-off-by: Kees Cook keescook@chromium.org Signed-off-by: Sasha Levin sashal@kernel.org --- fs/binfmt_elf.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c index e6c9c0e084486..ad01ba70a7baf 100644 --- a/fs/binfmt_elf.c +++ b/fs/binfmt_elf.c @@ -1312,6 +1312,9 @@ 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);