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Message-Id: <20180116223010.3066-1-daniel@iogearbox.net>
Date: Tue, 16 Jan 2018 23:30:10 +0100
From: Daniel Borkmann <daniel@...earbox.net>
To: alexei.starovoitov@...il.com
Cc: netdev@...r.kernel.org, Daniel Borkmann <daniel@...earbox.net>
Subject: [PATCH bpf] bpf: reject stores into ctx via st and xadd
Alexei found that verifier does not reject stores into context
via BPF_ST instead of BPF_STX. And while looking at it, we
also should not allow XADD variant of BPF_STX.
The context rewriter is only assuming either BPF_LDX_MEM- or
BPF_STX_MEM-type operations, thus reject anything other than
that so that assumptions in the rewriter properly hold. Add
test cases as well for BPF selftests.
Fixes: d691f9e8d440 ("bpf: allow programs to write to certain skb fields")
Reported-by: Alexei Starovoitov <ast@...nel.org>
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
---
kernel/bpf/verifier.c | 19 +++++++++++++++++++
tools/testing/selftests/bpf/test_verifier.c | 29 +++++++++++++++++++++++++++--
2 files changed, 46 insertions(+), 2 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 5423b90..1aff5de 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -978,6 +978,13 @@ static bool is_pointer_value(struct bpf_verifier_env *env, int regno)
return __is_pointer_value(env->allow_ptr_leaks, cur_regs(env) + regno);
}
+static bool is_ctx_reg(struct bpf_verifier_env *env, int regno)
+{
+ const struct bpf_reg_state *reg = cur_regs(env) + regno;
+
+ return reg->type == PTR_TO_CTX;
+}
+
static int check_pkt_ptr_alignment(struct bpf_verifier_env *env,
const struct bpf_reg_state *reg,
int off, int size, bool strict)
@@ -1258,6 +1265,12 @@ static int check_xadd(struct bpf_verifier_env *env, int insn_idx, struct bpf_ins
return -EACCES;
}
+ if (is_ctx_reg(env, insn->dst_reg)) {
+ verbose(env, "BPF_XADD stores into R%d context is not allowed\n",
+ insn->dst_reg);
+ return -EACCES;
+ }
+
/* check whether atomic_add can read the memory */
err = check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
BPF_SIZE(insn->code), BPF_READ, -1);
@@ -3991,6 +4004,12 @@ static int do_check(struct bpf_verifier_env *env)
if (err)
return err;
+ if (is_ctx_reg(env, insn->dst_reg)) {
+ verbose(env, "BPF_ST stores into R%d context is not allowed\n",
+ insn->dst_reg);
+ return -EACCES;
+ }
+
/* check that memory (dst_reg + off) is writeable */
err = check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
BPF_SIZE(insn->code), BPF_WRITE,
diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
index 74cb63e..c34d288 100644
--- a/tools/testing/selftests/bpf/test_verifier.c
+++ b/tools/testing/selftests/bpf/test_verifier.c
@@ -2593,6 +2593,29 @@ static struct bpf_test tests[] = {
.prog_type = BPF_PROG_TYPE_SCHED_CLS,
},
{
+ "context stores via ST",
+ .insns = {
+ BPF_MOV64_IMM(BPF_REG_0, 0),
+ BPF_ST_MEM(BPF_DW, BPF_REG_1, offsetof(struct __sk_buff, mark), 0),
+ BPF_EXIT_INSN(),
+ },
+ .errstr = "BPF_ST stores into R1 context is not allowed",
+ .result = REJECT,
+ .prog_type = BPF_PROG_TYPE_SCHED_CLS,
+ },
+ {
+ "context stores via XADD",
+ .insns = {
+ BPF_MOV64_IMM(BPF_REG_0, 0),
+ BPF_RAW_INSN(BPF_STX | BPF_XADD | BPF_W, BPF_REG_1,
+ BPF_REG_0, offsetof(struct __sk_buff, mark), 0),
+ BPF_EXIT_INSN(),
+ },
+ .errstr = "BPF_XADD stores into R1 context is not allowed",
+ .result = REJECT,
+ .prog_type = BPF_PROG_TYPE_SCHED_CLS,
+ },
+ {
"direct packet access: test1",
.insns = {
BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1,
@@ -4312,7 +4335,8 @@ static struct bpf_test tests[] = {
.fixup_map1 = { 2 },
.errstr_unpriv = "R2 leaks addr into mem",
.result_unpriv = REJECT,
- .result = ACCEPT,
+ .result = REJECT,
+ .errstr = "BPF_XADD stores into R1 context is not allowed",
},
{
"leak pointer into ctx 2",
@@ -4326,7 +4350,8 @@ static struct bpf_test tests[] = {
},
.errstr_unpriv = "R10 leaks addr into mem",
.result_unpriv = REJECT,
- .result = ACCEPT,
+ .result = REJECT,
+ .errstr = "BPF_XADD stores into R1 context is not allowed",
},
{
"leak pointer into ctx 3",
--
2.9.5
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