Commit 95a762e2 authored by Jann Horn's avatar Jann Horn Committed by Daniel Borkmann
Browse files

bpf: fix incorrect sign extension in check_alu_op()

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.

 - add CVE number (Ben Hutchings)

Fixes: 48461135

 ("bpf: allow access into map value arrays")
Signed-off-by: default avatarJann Horn <>
Acked-by: default avatarEdward Cree <>
Signed-off-by: default avatarAlexei Starovoitov <>
Signed-off-by: default avatarDaniel Borkmann <>
parent 4374f256
......@@ -2408,7 +2408,13 @@ 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,
} else {
__mark_reg_known(regs + insn->dst_reg,
} else if (opcode > BPF_END) {
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