From: Jann Horn jannh@google.com
[ Upstream commit 95a762e2c8c942780948091f8f2a4f32fce1ac6f ]
Distinguish between BPF_ALU64|BPF_MOV|BPF_K (load 32-bit immediate, sign-extended to 64-bit) and BPF_ALU|BPF_MOV|BPF_K (load 32-bit immediate, zero-padded to 64-bit); only perform sign extension in the first case.
Starting with v4.14, this is exploitable by unprivileged users as long as the unprivileged_bpf_disabled sysctl isn't set.
Debian assigned CVE-2017-16995 for this issue.
v3: - add CVE number (Ben Hutchings)
Fixes: 484611357c19 ("bpf: allow access into map value arrays") Signed-off-by: Jann Horn jannh@google.com Acked-by: Edward Cree ecree@solarflare.com Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Daniel Borkmann daniel@iogearbox.net --- kernel/bpf/verifier.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index c6ec04f..2811ced 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2374,7 +2374,13 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn) * remember the value we stored into this reg */ regs[insn->dst_reg].type = SCALAR_VALUE; - __mark_reg_known(regs + insn->dst_reg, insn->imm); + if (BPF_CLASS(insn->code) == BPF_ALU64) { + __mark_reg_known(regs + insn->dst_reg, + insn->imm); + } else { + __mark_reg_known(regs + insn->dst_reg, + (u32)insn->imm); + } }
} else if (opcode > BPF_END) {