[PATCH bpf-next 2/2] bpf: prevent decl_tag from being referenced in func_proto arg

[Stanislav Fomichev <sdf@google.com>]

Syzkaller managed to hit anoher decl_tag issue:

 btf_func_proto_check kernel/bpf/btf.c:4506 [inline]
 btf_check_all_types kernel/bpf/btf.c:4734 [inline]
 btf_parse_type_sec+0x1175/0x1980 kernel/bpf/btf.c:4763
 btf_parse kernel/bpf/btf.c:5042 [inline]
 btf_new_fd+0x65a/0xb00 kernel/bpf/btf.c:6709
 bpf_btf_load+0x6f/0x90 kernel/bpf/syscall.c:4342
 __sys_bpf+0x50a/0x6c0 kernel/bpf/syscall.c:5034
 __do_sys_bpf kernel/bpf/syscall.c:5093 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:5091 [inline]
 __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:5091
 do_syscall_64+0x54/0x70 arch/x86/entry/common.c:48

This seems similar to commit ea68376c8bed ("bpf: prevent decl_tag from
being referenced in func_proto") but for the argument.

Reported-by: syzbot+8dd0551dda6020944c5d@syzkaller.appspotmail.com
Signed-off-by: Stanislav Fomichev <sdf@google.com>
---
 kernel/bpf/btf.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 1a59cc7ad730..cb43cb842e16 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -4792,6 +4792,11 @@ static int btf_func_proto_check(struct btf_verifier_env *env,
 			break;
 		}
 
+		if (btf_type_is_resolve_source_only(arg_type)) {
+			btf_verifier_log_type(env, t, "Invalid arg#%u", i + 1);
+			return -EINVAL;
+		}
+
 		if (args[i].name_off &&
 		    (!btf_name_offset_valid(btf, args[i].name_off) ||
 		     !btf_name_valid_identifier(btf, args[i].name_off))) {
-- 
2.38.1.584.g0f3c55d4c2-goog