From: Daniel Borkmann daniel@iogearbox.net
commit f37a8cb84cce18762e8f86a70bd6a49a66ab964c upstream.
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 [bwh: Backported to 4.4: - Drop selftest changes - verbose() doesn't take an env pointer - s/bpf_verifier_env/verifier_env/; s/bpf_reg_state/reg_state/ - Open-code cur_regs()] Signed-off-by: Ben Hutchings ben.hutchings@codethink.co.uk --- kernel/bpf/verifier.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 32af15136bf4..bb3e96628228 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -683,6 +683,13 @@ static bool is_pointer_value(struct verifier_env *env, int regno) } }
+static bool is_ctx_reg(struct verifier_env *env, int regno) +{ + const struct reg_state *reg = env->cur_state.regs + regno; + + return reg->type == PTR_TO_CTX; +} + /* check whether memory at (regno + off) is accessible for t = (read | write) * if t==write, value_regno is a register which value is stored into memory * if t==read, value_regno is a register which will receive the value from memory @@ -779,6 +786,12 @@ static int check_xadd(struct verifier_env *env, struct bpf_insn *insn) 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->dst_reg, insn->off, BPF_SIZE(insn->code), BPF_READ, -1); @@ -1909,6 +1922,12 @@ static int do_check(struct 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->dst_reg, insn->off, BPF_SIZE(insn->code), BPF_WRITE,