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bpf: fix incorrect sign extension in check_alu_op()

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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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Daniel Borkmann 2017-12-22 16:29:05 +01:00 committed by Greg Kroah-Hartman
parent d75d3ee237
commit 3695b3b185
1 changed files with 10 additions and 3 deletions
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13
kernel/bpf/verifier.c
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@ -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) {