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bpf: enable verifier to add 0 to packet ptr 

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 <u9012063@gmail.com>
Signed-off-by: Mihai Budiu <mbudiu@vmware.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
William Tu 2017-02-04 08:37:29 -08:00 committed by David S. Miller
parent 29200c199c
commit 63dfef75ed
2 changed files with 24 additions and 1 deletions
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2
kernel/bpf/verifier.c
View File

@ -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;
}

23
tools/testing/selftests/bpf/test_verifier.c
View File

@ -2403,6 +2403,29 @@ static struct bpf_test tests[] = {
.result = ACCEPT,
.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 = {