The patch fixes the case when adding a zero value to the packet
pointer. The zero value could come from src_reg equals type
BPF_K or CONST_IMM. The patch fixes both, otherwise the verifer
reports the following error:
[...]
R0=imm0,min_value=0,max_value=0
R1=pkt(id=0,off=0,r=4)
R2=pkt_end R3=fp-12
R4=imm4,min_value=4,max_value=4
R5=pkt(id=0,off=4,r=4)
269: (bf) r2 = r0 // r2 becomes imm0
270: (77) r2 >>= 3
271: (bf) r4 = r1 // r4 becomes pkt ptr
272: (0f) r4 += r2 // r4 += 0
addition of negative constant to packet pointer is not allowed
Signed-off-by: William Tu <u9012...@gmail.com>
Signed-off-by: Mihai Budiu <mbu...@vmware.com>
Cc: Daniel Borkmann <dan...@iogearbox.net>
Cc: Alexei Starovoitov <a...@kernel.org>
Acked-by: Daniel Borkmann <dan...@iogearbox.net>
---
kernel/bpf/verifier.c | 2 +-
tools/testing/selftests/bpf/test_verifier.c | 23 +++++++++++++++++++++++
2 files changed, 24 insertions(+), 1 deletion(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index fb3513b..1a754e5 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1397,7 +1397,7 @@ static int check_packet_ptr_add(struct bpf_verifier_env
*env,
imm = insn->imm;
add_imm:
- if (imm <= 0) {
+ if (imm < 0) {
verbose("addition of negative constant to packet
pointer is not allowed\n");
return -EACCES;
}
diff --git a/tools/testing/selftests/bpf/test_verifier.c
b/tools/testing/selftests/bpf/test_verifier.c
index 0d0912c..c841e5f 100644
--- a/tools/testing/selftests/bpf/test_verifier.c
+++ b/tools/testing/selftests/bpf/test_verifier.c
@@ -2404,6 +2404,29 @@ static struct bpf_test tests[] = {
.prog_type = BPF_PROG_TYPE_SCHED_CLS,
},
{
+ "direct packet access: test14 (pkt_ptr += 0, CONST_IMM, good
access)",
+ .insns = {
+ BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1,
+ offsetof(struct __sk_buff, data)),
+ BPF_LDX_MEM(BPF_W, BPF_REG_3, BPF_REG_1,
+ offsetof(struct __sk_buff, data_end)),
+ BPF_MOV64_REG(BPF_REG_0, BPF_REG_2),
+ BPF_ALU64_IMM(BPF_ADD, BPF_REG_0, 22),
+ BPF_JMP_REG(BPF_JGT, BPF_REG_0, BPF_REG_3, 7),
+ BPF_MOV64_IMM(BPF_REG_5, 12),
+ BPF_ALU64_IMM(BPF_RSH, BPF_REG_5, 4),
+ BPF_MOV64_REG(BPF_REG_6, BPF_REG_2),
+ BPF_ALU64_REG(BPF_ADD, BPF_REG_6, BPF_REG_5),
+ BPF_LDX_MEM(BPF_B, BPF_REG_0, BPF_REG_6, 0),
+ BPF_MOV64_IMM(BPF_REG_0, 1),
+ BPF_EXIT_INSN(),
+ BPF_MOV64_IMM(BPF_REG_0, 0),
+ BPF_EXIT_INSN(),
+ },
+ .result = ACCEPT,
+ .prog_type = BPF_PROG_TYPE_SCHED_CLS,
+ },
+ {
"helper access to packet: test1, valid packet_ptr range",
.insns = {
BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1,
--
2.7.4
