From c96c67991aac6401b4c6996093bccb704bb2ea4b Mon Sep 17 00:00:00 2001 From: Yafang Shao Date: Wed, 23 Aug 2023 02:07:02 +0000 Subject: [PATCH] bpf: Fix issue in verifying allow_ptr_leaks commit d75e30dddf73449bc2d10bb8e2f1a2c446bc67a2 upstream. After we converted the capabilities of our networking-bpf program from cap_sys_admin to cap_net_admin+cap_bpf, our networking-bpf program failed to start. Because it failed the bpf verifier, and the error log is "R3 pointer comparison prohibited". A simple reproducer as follows, SEC("cls-ingress") int ingress(struct __sk_buff *skb) { struct iphdr *iph = (void *)(long)skb->data + sizeof(struct ethhdr); if ((long)(iph + 1) > (long)skb->data_end) return TC_ACT_STOLEN; return TC_ACT_OK; } Per discussion with Yonghong and Alexei [1], comparison of two packet pointers is not a pointer leak. This patch fixes it. Our local kernel is 6.1.y and we expect this fix to be backported to 6.1.y, so stable is CCed. [1]. https://lore.kernel.org/bpf/CAADnVQ+Nmspr7Si+pxWn8zkE7hX-7s93ugwC+94aXSy4uQ9vBg@mail.gmail.com/ Suggested-by: Yonghong Song Suggested-by: Alexei Starovoitov Signed-off-by: Yafang Shao Acked-by: Eduard Zingerman Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20230823020703.3790-2-laoar.shao@gmail.com Signed-off-by: Alexei Starovoitov Signed-off-by: Greg Kroah-Hartman --- kernel/bpf/verifier.c | 17 +++++++++-------- 1 file changed, 9 insertions(+), 8 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 3c414e0ac819..3052680201e5 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -10401,6 +10401,12 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env, return -EINVAL; } + /* check src2 operand */ + err = check_reg_arg(env, insn->dst_reg, SRC_OP); + if (err) + return err; + + dst_reg = ®s[insn->dst_reg]; if (BPF_SRC(insn->code) == BPF_X) { if (insn->imm != 0) { verbose(env, "BPF_JMP/JMP32 uses reserved fields\n"); @@ -10412,12 +10418,13 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env, if (err) return err; - if (is_pointer_value(env, insn->src_reg)) { + src_reg = ®s[insn->src_reg]; + if (!(reg_is_pkt_pointer_any(dst_reg) && reg_is_pkt_pointer_any(src_reg)) && + is_pointer_value(env, insn->src_reg)) { verbose(env, "R%d pointer comparison prohibited\n", insn->src_reg); return -EACCES; } - src_reg = ®s[insn->src_reg]; } else { if (insn->src_reg != BPF_REG_0) { verbose(env, "BPF_JMP/JMP32 uses reserved fields\n"); @@ -10425,12 +10432,6 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env, } } - /* check src2 operand */ - err = check_reg_arg(env, insn->dst_reg, SRC_OP); - if (err) - return err; - - dst_reg = ®s[insn->dst_reg]; is_jmp32 = BPF_CLASS(insn->code) == BPF_JMP32; if (BPF_SRC(insn->code) == BPF_K) {