From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Yonghong Song <yhs@fb.com>
Cc: Kurt Manucredo <fuzzybritches0@gmail.com>,
syzbot+bed360704c521841c85d@syzkaller.appspotmail.com,
Andrii Nakryiko <andrii@kernel.org>,
Alexei Starovoitov <ast@kernel.org>, bpf <bpf@vger.kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
"David S. Miller" <davem@davemloft.net>,
Jesper Dangaard Brouer <hawk@kernel.org>,
John Fastabend <john.fastabend@gmail.com>,
Martin KaFai Lau <kafai@fb.com>, KP Singh <kpsingh@kernel.org>,
Jakub Kicinski <kuba@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Network Development <netdev@vger.kernel.org>,
Song Liu <songliubraving@fb.com>,
syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
nathan@kernel.org, Nick Desaulniers <ndesaulniers@google.com>,
Clang-Built-Linux ML <clang-built-linux@googlegroups.com>,
linux-kernel-mentees@lists.linuxfoundation.org,
Shuah Khan <skhan@linuxfoundation.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH v4] bpf: core: fix shift-out-of-bounds in ___bpf_prog_run
Date: Sat, 5 Jun 2021 12:10:26 -0700 [thread overview]
Message-ID: <CAADnVQKexxZQw0yK_7rmFOdaYabaFpi2EmF6RGs5bXvFHtUQaA@mail.gmail.com> (raw)
In-Reply-To: <6a392b66-6f26-4532-d25f-6b09770ce366@fb.com>
On Sat, Jun 5, 2021 at 10:55 AM Yonghong Song <yhs@fb.com> wrote:
>
>
>
> On 6/5/21 8:01 AM, Kurt Manucredo wrote:
> > Syzbot detects a shift-out-of-bounds in ___bpf_prog_run()
> > kernel/bpf/core.c:1414:2.
>
> This is not enough. We need more information on why this happens
> so we can judge whether the patch indeed fixed the issue.
>
> >
> > I propose: In adjust_scalar_min_max_vals() move boundary check up to avoid
> > missing them and return with error when detected.
> >
> > Reported-and-tested-by: syzbot+bed360704c521841c85d@syzkaller.appspotmail.com
> > Signed-off-by: Kurt Manucredo <fuzzybritches0@gmail.com>
> > ---
> >
> > https://syzkaller.appspot.com/bug?id=edb51be4c9a320186328893287bb30d5eed09231
> >
> > Changelog:
> > ----------
> > v4 - Fix shift-out-of-bounds in adjust_scalar_min_max_vals.
> > Fix commit message.
> > v3 - Make it clearer what the fix is for.
> > v2 - Fix shift-out-of-bounds in ___bpf_prog_run() by adding boundary
> > check in check_alu_op() in verifier.c.
> > v1 - Fix shift-out-of-bounds in ___bpf_prog_run() by adding boundary
> > check in ___bpf_prog_run().
> >
> > thanks
> >
> > kind regards
> >
> > Kurt
> >
> > kernel/bpf/verifier.c | 30 +++++++++---------------------
> > 1 file changed, 9 insertions(+), 21 deletions(-)
> >
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index 94ba5163d4c5..ed0eecf20de5 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -7510,6 +7510,15 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
> > u32_min_val = src_reg.u32_min_value;
> > u32_max_val = src_reg.u32_max_value;
> >
> > + if ((opcode == BPF_LSH || opcode == BPF_RSH || opcode == BPF_ARSH) &&
> > + umax_val >= insn_bitness) {
> > + /* Shifts greater than 31 or 63 are undefined.
> > + * This includes shifts by a negative number.
> > + */
> > + verbose(env, "invalid shift %lld\n", umax_val);
> > + return -EINVAL;
> > + }
>
> I think your fix is good. I would like to move after
I suspect such change will break valid programs that do shift by register.
> the following code though:
>
> if (!src_known &&
> opcode != BPF_ADD && opcode != BPF_SUB && opcode != BPF_AND) {
> __mark_reg_unknown(env, dst_reg);
> return 0;
> }
>
> > +
> > if (alu32) {
> > src_known = tnum_subreg_is_const(src_reg.var_off);
> > if ((src_known &&
> > @@ -7592,39 +7601,18 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
> > scalar_min_max_xor(dst_reg, &src_reg);
> > break;
> > case BPF_LSH:
> > - if (umax_val >= insn_bitness) {
> > - /* Shifts greater than 31 or 63 are undefined.
> > - * This includes shifts by a negative number.
> > - */
> > - mark_reg_unknown(env, regs, insn->dst_reg);
> > - break;
> > - }
>
> I think this is what happens. For the above case, we simply
> marks the dst reg as unknown and didn't fail verification.
> So later on at runtime, the shift optimization will have wrong
> shift value (> 31/64). Please correct me if this is not right
> analysis. As I mentioned in the early please write detailed
> analysis in commit log.
The large shift is not wrong. It's just undefined.
syzbot has to ignore such cases.
next prev parent reply other threads:[~2021-06-05 19:11 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-10 16:05 [syzbot] UBSAN: shift-out-of-bounds in ___bpf_prog_run syzbot
2021-03-28 3:38 ` syzbot
2021-06-02 21:27 ` [PATCH v3] bpf: core: fix " Kurt Manucredo
2021-06-03 4:43 ` Greg KH
2021-06-05 15:01 ` [PATCH v4] " Kurt Manucredo
2021-06-05 17:55 ` Yonghong Song
2021-06-05 19:10 ` Alexei Starovoitov [this message]
2021-06-05 21:39 ` Yonghong Song
2021-06-06 19:44 ` Kurt Manucredo
2021-06-07 7:38 ` Dmitry Vyukov
2021-06-09 18:20 ` Kees Cook
2021-06-09 23:40 ` Yonghong Song
2021-06-10 5:32 ` Dmitry Vyukov
2021-06-10 6:06 ` Yonghong Song
2021-06-10 17:06 ` Kees Cook
2021-06-10 17:52 ` Alexei Starovoitov
2021-06-10 20:00 ` Eric Biggers
2021-06-15 16:42 ` [PATCH v5] " Kurt Manucredo
2021-06-15 18:51 ` Edward Cree
2021-06-15 19:33 ` Eric Biggers
2021-06-15 21:08 ` Daniel Borkmann
2021-06-15 21:32 ` Eric Biggers
2021-06-15 21:38 ` Eric Biggers
2021-06-15 21:54 ` Daniel Borkmann
2021-06-15 22:07 ` Eric Biggers
2021-06-15 22:31 ` Kurt Manucredo
2021-06-17 10:09 ` Daniel Borkmann
2021-06-06 19:15 ` [PATCH v4] " Kurt Manucredo
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAADnVQKexxZQw0yK_7rmFOdaYabaFpi2EmF6RGs5bXvFHtUQaA@mail.gmail.com \
--to=alexei.starovoitov@gmail.com \
--cc=andrii@kernel.org \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=clang-built-linux@googlegroups.com \
--cc=daniel@iogearbox.net \
--cc=davem@davemloft.net \
--cc=fuzzybritches0@gmail.com \
--cc=gregkh@linuxfoundation.org \
--cc=hawk@kernel.org \
--cc=john.fastabend@gmail.com \
--cc=kafai@fb.com \
--cc=kpsingh@kernel.org \
--cc=kuba@kernel.org \
--cc=linux-kernel-mentees@lists.linuxfoundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=nathan@kernel.org \
--cc=ndesaulniers@google.com \
--cc=netdev@vger.kernel.org \
--cc=skhan@linuxfoundation.org \
--cc=songliubraving@fb.com \
--cc=syzbot+bed360704c521841c85d@syzkaller.appspotmail.com \
--cc=syzkaller-bugs@googlegroups.com \
--cc=yhs@fb.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).