[PATCH bpf-next] bpf: remove WARN_ON_ONCE from btf_type_id_size

[Stanislav Fomichev <sdf@google.com>]

Syzkaller was able to hit it with the following reproducer:

bpf$BPF_BTF_LOAD(0x12, &(0x7f0000000140)={&(0x7f0000001680)={{0xeb9f, 0x1, 0x0, 0x18, 0x0, 0x34, 0x34, 0xc, [@fwd={0xa}, @var={0x3, 0x0, 0x0, 0x11, 0x4, 0xffffffff}, @func_proto={0x0, 0x0, 0x0, 0xd, 0x2}, @struct]}, {0x0, [0x0, 0x0, 0x5f, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x6c]}}, &(0x7f00000004c0)=""/4096, 0x58, 0x1000, 0x1}, 0x20)

------------[ cut here ]------------
WARNING: CPU: 0 PID: 3609 at kernel/bpf/btf.c:1946
btf_type_id_size+0x2d5/0x9d0 kernel/bpf/btf.c:1946
Modules linked in:
CPU: 0 PID: 3609 Comm: syz-executor361 Not tainted
6.0.0-syzkaller-02734-g0326074ff465 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 09/22/2022
RIP: 0010:btf_type_id_size+0x2d5/0x9d0 kernel/bpf/btf.c:1946
Code: ef e8 7f 8e e4 ff 41 83 ff 0b 77 28 f6 44 24 10 18 75 3f e8 6d 91
e4 ff 44 89 fe bf 0e 00 00 00 e8 20 8e e4 ff e8 5b 91 e4 ff <0f> 0b 45
31 f6 e9 98 02 00 00 41 83 ff 12 74 18 e8 46 91 e4 ff 44
RSP: 0018:ffffc90003cefb40 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 0000000000000002 RCX: 0000000000000000
RDX: ffff8880259c0000 RSI: ffffffff81968415 RDI: 0000000000000005
RBP: ffff88801270ca00 R08: 0000000000000005 R09: 000000000000000e
R10: 0000000000000011 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000011 R14: ffff888026ee6424 R15: 0000000000000011
FS:  000055555641b300(0000) GS:ffff8880b9a00000(0000)
knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000f2e258 CR3: 000000007110e000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 btf_func_proto_check kernel/bpf/btf.c:4447 [inline]
 btf_check_all_types kernel/bpf/btf.c:4723 [inline]
 btf_parse_type_sec kernel/bpf/btf.c:4752 [inline]
 btf_parse kernel/bpf/btf.c:5026 [inline]
 btf_new_fd+0x1926/0x1e70 kernel/bpf/btf.c:6892
 bpf_btf_load kernel/bpf/syscall.c:4324 [inline]
 __sys_bpf+0xb7d/0x4cf0 kernel/bpf/syscall.c:5010
 __do_sys_bpf kernel/bpf/syscall.c:5069 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:5067 [inline]
 __x64_sys_bpf+0x75/0xb0 kernel/bpf/syscall.c:5067
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f0fbae41c69
Code: 28 c3 e8 2a 14 00 00 66 2e 0f 1f 84 00 00 00 00 00 48 89 f8 48 89
f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01
f0 ff ff 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffc8aeb6228 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f0fbae41c69
RDX: 0000000000000020 RSI: 0000000020000140 RDI: 0000000000000012
RBP: 00007f0fbae05e10 R08: 0000000000000000 R09: 0000000000000000
R10: 00000000ffffffff R11: 0000000000000246 R12: 00007f0fbae05ea0
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 </TASK>

Any reason we need that WARN_ON_ONCE in this place?
All callers except btf_array_check_member check the return value,
so it should be safe. Assuming btf_array_check_member should also be fine
because it hits 'btf_type_is_array()' condition.

Reported-by: syzbot+d8bd751aef7c6b39a344@syzkaller.appspotmail.com
Signed-off-by: Stanislav Fomichev <sdf@google.com>
---
 kernel/bpf/btf.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index eba603cec2c5..999f62c697a7 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -1943,8 +1943,8 @@ const struct btf_type *btf_type_id_size(const struct btf *btf,
 	} else if (btf_type_is_ptr(size_type)) {
 		size = sizeof(void *);
 	} else {
-		if (WARN_ON_ONCE(!btf_type_is_modifier(size_type) &&
-				 !btf_type_is_var(size_type)))
+		if (!btf_type_is_modifier(size_type) &&
+		    !btf_type_is_var(size_type))
 			return NULL;
 
 		size_type_id = btf_resolved_type_id(btf, size_type_id);
-- 
2.38.0.rc1.362.ged0d419d3c-goog