6.4-stable review patch. If anyone has any objections, please let me know.
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From: Yafang Shao laoar.shao@gmail.com
[ Upstream commit 7ce4dc3e4a9d954c8a1fb483c7a527e9b060b860 ]
Per discussion with Alexei, the PTR_UNTRUSTED flag should not been cleared when we start to walk a new struct, because the struct in question may be a struct nested in a union. We should also check and set this flag before we walk its each member, in case itself is a union. We will clear this flag if the field is BTF_TYPE_SAFE_RCU_OR_NULL.
Fixes: 6fcd486b3a0a ("bpf: Refactor RCU enforcement in the verifier.") Signed-off-by: Yafang Shao laoar.shao@gmail.com Link: https://lore.kernel.org/r/20230713025642.27477-2-laoar.shao@gmail.com Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/btf.c | 20 +++++++++----------- kernel/bpf/verifier.c | 5 +++++ 2 files changed, 14 insertions(+), 11 deletions(-)
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index 8b4e92439d1d6..5dd8534b778d1 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -6126,7 +6126,6 @@ static int btf_struct_walk(struct bpf_verifier_log *log, const struct btf *btf, const char *tname, *mname, *tag_value; u32 vlen, elem_id, mid;
- *flag = 0; again: tname = __btf_name_by_offset(btf, t->name_off); if (!btf_type_is_struct(t)) { @@ -6135,6 +6134,14 @@ static int btf_struct_walk(struct bpf_verifier_log *log, const struct btf *btf, }
vlen = btf_type_vlen(t); + if (BTF_INFO_KIND(t->info) == BTF_KIND_UNION && vlen != 1 && !(*flag & PTR_UNTRUSTED)) + /* + * walking unions yields untrusted pointers + * with exception of __bpf_md_ptr and other + * unions with a single member + */ + *flag |= PTR_UNTRUSTED; + if (off + size > t->size) { /* If the last element is a variable size array, we may * need to relax the rule. @@ -6295,15 +6302,6 @@ static int btf_struct_walk(struct bpf_verifier_log *log, const struct btf *btf, * of this field or inside of this struct */ if (btf_type_is_struct(mtype)) { - if (BTF_INFO_KIND(mtype->info) == BTF_KIND_UNION && - btf_type_vlen(mtype) != 1) - /* - * walking unions yields untrusted pointers - * with exception of __bpf_md_ptr and other - * unions with a single member - */ - *flag |= PTR_UNTRUSTED; - /* our field must be inside that union or struct */ t = mtype;
@@ -6469,7 +6467,7 @@ bool btf_struct_ids_match(struct bpf_verifier_log *log, bool strict) { const struct btf_type *type; - enum bpf_type_flag flag; + enum bpf_type_flag flag = 0; int err;
/* Are we already done? */ diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 4fbfe1d086467..cef173614fc8f 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -5893,6 +5893,11 @@ static int check_ptr_to_btf_access(struct bpf_verifier_env *env, type_is_rcu_or_null(env, reg, field_name, btf_id)) { /* __rcu tagged pointers can be NULL */ flag |= MEM_RCU | PTR_MAYBE_NULL; + + /* We always trust them */ + if (type_is_rcu_or_null(env, reg, field_name, btf_id) && + flag & PTR_UNTRUSTED) + flag &= ~PTR_UNTRUSTED; } else if (flag & (MEM_PERCPU | MEM_USER)) { /* keep as-is */ } else {