[ upstream commit f37a8cb84cce18762e8f86a70bd6a49a66ab964c ]
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@kernel.org Signed-off-by: Daniel Borkmann daniel@iogearbox.net Signed-off-by: Alexei Starovoitov ast@kernel.org --- 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 ab2be68..f9339c3 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -986,6 +986,13 @@ static bool is_pointer_value(struct bpf_verifier_env *env, int regno) return __is_pointer_value(env->allow_ptr_leaks, &env->cur_state.regs[regno]); }
+static bool is_ctx_reg(struct bpf_verifier_env *env, int regno) +{ + const struct bpf_reg_state *reg = &env->cur_state.regs[regno]; + + return reg->type == PTR_TO_CTX; +} + static int check_pkt_ptr_alignment(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("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); @@ -3859,6 +3872,12 @@ static int do_check(struct bpf_verifier_env *env) if (err) return err;
+ if (is_ctx_reg(env, insn->dst_reg)) { + verbose("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 1241487..1629993 100644 --- a/tools/testing/selftests/bpf/test_verifier.c +++ b/tools/testing/selftests/bpf/test_verifier.c @@ -2596,6 +2596,29 @@ 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, @@ -4317,7 +4340,8 @@ 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", @@ -4331,7 +4355,8 @@ 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",