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| author | Daniel Borkmann <daniel@iogearbox.net> | 2018-01-16 23:30:10 +0100 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2018-01-16 15:04:58 -0800 |
| commit | f37a8cb84cce18762e8f86a70bd6a49a66ab964c (patch) | |
| tree | d6440b185e4d4810624fb59163ff419cd1a28ca4 /kernel | |
| parent | a2284d912bfc865cdca4c00488e08a3550f9a405 (diff) | |
| download | linux-f37a8cb84cce18762e8f86a70bd6a49a66ab964c.tar.bz2 | |
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@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/bpf/verifier.c | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index b7448347e6b6..eb062b0fbf27 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); @@ -3993,6 +4006,12 @@ 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, |