bpf: Loosen alloc obj test in verifier's reg_btf_record

btf->struct_meta_tab is populated by btf_parse_struct_metas in btf.c.
There, a BTF record is created for any type containing a spin_lock or
any next-gen datastructure node/head.

Currently, for non-MAP_VALUE types, reg_btf_record will only search for
a record using struct_meta_tab if the reg->type exactly matches
(PTR_TO_BTF_ID | MEM_ALLOC). This exact match is too strict: an
"allocated obj" type - returned from bpf_obj_new - might pick up other
flags while working its way through the program.

Loosen the check to be exact for base_type and just use MEM_ALLOC mask
for type_flag.

This patch is marked Fixes as the original intent of reg_btf_record was
unlikely to have been to fail finding btf_record for valid alloc obj
types with additional flags, some of which (e.g. PTR_UNTRUSTED)
are valid register type states for alloc obj independent of this series.
However, I didn't find a specific broken repro case outside of this
series' added functionality, so it's possible that nothing was
triggering this logic error before.

Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
cc: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Fixes: 4e814da ("bpf: Allow locking bpf_spin_lock in allocated objects")
Link: https://lore.kernel.org/r/20221206231000.3180914-2-davemarchevsky@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: davemarchevsky

kernel/bpf/verifier.c

@@ -451,14 +451,19 @@ static bool reg_type_not_null(enum bpf_reg_type type)
 		type == PTR_TO_SOCK_COMMON;
 }
 
+static bool type_is_ptr_alloc_obj(u32 type)
+{
+	return base_type(type) == PTR_TO_BTF_ID && type_flag(type) & MEM_ALLOC;
+}
+
 static struct btf_record *reg_btf_record(const struct bpf_reg_state *reg)
 {
 	struct btf_record *rec = NULL;
 	struct btf_struct_meta *meta;
 
 	if (reg->type == PTR_TO_MAP_VALUE) {
 		rec = reg->map_ptr->record;
-	} else if (reg->type == (PTR_TO_BTF_ID | MEM_ALLOC)) {
+	} else if (type_is_ptr_alloc_obj(reg->type)) {
 		meta = btf_find_struct_meta(reg->btf, reg->btf_id);
 		if (meta)
 			rec = meta->record;