From: Jann Horn <jannh@xxxxxxxxxx>
[ 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@xxxxxxxxxx>
Acked-by: Edward Cree <ecree@xxxxxxxxxxxxxx>
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
---
kernel/bpf/verifier.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index b03af36..8b1ebe4 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1790,10 +1790,17 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn)
/* case: R = imm
* remember the value we stored into this reg
*/
+ u64 imm;
+
+ if (BPF_CLASS(insn->code) == BPF_ALU64)
+ imm = insn->imm;
+ else
+ imm = (u32)insn->imm;
+
regs[insn->dst_reg].type = CONST_IMM;
- regs[insn->dst_reg].imm = insn->imm;
- regs[insn->dst_reg].max_value = insn->imm;
- regs[insn->dst_reg].min_value = insn->imm;
+ regs[insn->dst_reg].imm = imm;
+ regs[insn->dst_reg].max_value = imm;
+ regs[insn->dst_reg].min_value = imm;
}
} else if (opcode > BPF_END) {
--
2.9.5