patches/kernel/0227-bpf-fix-incorrect-sign-extension-in-check_alu_op.patch

   1 From 652c6cabaf30e4c75f7dc2c42a33a8f066d7df2c Mon Sep 17 00:00:00 2001
   2 From: Jann Horn <jannh@google.com>
   3 Date: Thu, 4 Jan 2018 08:01:22 -0600
   4 Subject: [PATCH 227/233] bpf: fix incorrect sign extension in check_alu_op()
   5 MIME-Version: 1.0
   6 Content-Type: text/plain; charset=UTF-8
   7 Content-Transfer-Encoding: 8bit
   8
   9 [ Upstream commit 95a762e2c8c942780948091f8f2a4f32fce1ac6f ]
  10
  11 Distinguish between
  12 BPF_ALU64|BPF_MOV|BPF_K (load 32-bit immediate, sign-extended to 64-bit)
  13 and BPF_ALU|BPF_MOV|BPF_K (load 32-bit immediate, zero-padded to 64-bit);
  14 only perform sign extension in the first case.
  15
  16 Starting with v4.14, this is exploitable by unprivileged users as long as
  17 the unprivileged_bpf_disabled sysctl isn't set.
  18
  19 Debian assigned CVE-2017-16995 for this issue.
  20
  21 v3:
  22  - add CVE number (Ben Hutchings)
  23
  24 Fixes: 484611357c19 ("bpf: allow access into map value arrays")
  25 Signed-off-by: Jann Horn <jannh@google.com>
  26 Acked-by: Edward Cree <ecree@solarflare.com>
  27 Signed-off-by: Alexei Starovoitov <ast@kernel.org>
  28 Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
  29 CVE-2017-16995
  30 Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
  31 Signed-off-by: Andy Whitcroft <apw@canonical.com>
  32 Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
  33 (cherry picked from commit 868c88129c7567525dbde3cb6989a5acd478bd80)
  34 Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
  35 ---
  36  kernel/bpf/verifier.c | 15 +++++++++++----
  37  1 file changed, 11 insertions(+), 4 deletions(-)
  38
  39 diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
  40 index 4321625fe32a..cdfa07a4ef27 100644
  41 --- a/kernel/bpf/verifier.c
  42 +++ b/kernel/bpf/verifier.c
  43 @@ -2048,12 +2048,19 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn)
  44                         /* case: R = imm
  45                          * remember the value we stored into this reg
  46                          */
  47 +                       u64 imm;
  48 +
  49 +                       if (BPF_CLASS(insn->code) == BPF_ALU64)
  50 +                               imm = insn->imm;
  51 +                       else
  52 +                               imm = (u32)insn->imm;
  53 +
  54                         regs[insn->dst_reg].type = CONST_IMM;
  55 -                       regs[insn->dst_reg].imm = insn->imm;
  56 +                       regs[insn->dst_reg].imm = imm;
  57                         regs[insn->dst_reg].id = 0;
  58 -                       regs[insn->dst_reg].max_value = insn->imm;
  59 -                       regs[insn->dst_reg].min_value = insn->imm;
  60 -                       regs[insn->dst_reg].min_align = calc_align(insn->imm);
  61 +                       regs[insn->dst_reg].max_value = imm;
  62 +                       regs[insn->dst_reg].min_value = imm;
  63 +                       regs[insn->dst_reg].min_align = calc_align(imm);
  64                         regs[insn->dst_reg].value_from_signed = false;
  65                 }
  66
  67 --
  68 2.14.2
  69