[ 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@xxxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
---
kernel/bpf/verifier.c | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index c9156bd..c140038 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,
--
2.9.5