From 7435fa1c530d01b6f90d7a7524b1ec01e2c00dd8 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Fri, 16 Feb 2024 22:25:44 -0800 Subject: [PATCH] binfmt_elf: Leave a gap between .bss and brk [ 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: 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 Stable-dep-of: 11854fe263eb ("binfmt_elf: Move brk for static PIE even if ASLR disabled") Signed-off-by: Sasha Levin --- fs/binfmt_elf.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c index 02258b28e370..700d93e73f6e 100644 --- a/fs/binfmt_elf.c +++ b/fs/binfmt_elf.c @@ -1293,6 +1293,9 @@ out_free_interp: 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);