| Message ID | 20240217062545.1631668-2-keescook@chromium.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Adjust brk randomness | expand |
On Fri, 16 Feb 2024 22:25:44 -0800, Kees Cook wrote: > 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). > > > [...] Patch 1/2 was already applied via x86 tip, so I'll grab this one for the execve/binfmt tree. Applied to for-next/execve. [2/2] binfmt_elf: Leave a gap between .bss and brk https://git.kernel.org/kees/c/2a5eb9995528 Take care,
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c index 5397b552fbeb..7862962f7a85 100644 --- a/fs/binfmt_elf.c +++ b/fs/binfmt_elf.c @@ -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);
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/ Signed-off-by: Kees Cook <keescook@chromium.org> --- Cc: Jiri Kosina <jikos@kernel.org> Cc: Geert Uytterhoeven <geert@linux-m68k.org> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Christian Brauner <brauner@kernel.org> Cc: Jan Kara <jack@suse.cz> Cc: Eric Biederman <ebiederm@xmission.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: linux-fsdevel@vger.kernel.org Cc: linux-mm@kvack.org --- fs/binfmt_elf.c | 3 +++ 1 file changed, 3 insertions(+)