Blamed commit added these helpers for sake of detecting RAW
sockets specific ioctl.

syzbot complained about it [1].

Issue here is that RAW sockets could pretend there was no need
to call ipmr_sk_ioctl()

Regardless of inet_sk(sk)->inet_num, we must be prepared
for ipmr_ioctl() being called later. This must happen
from ipmr_sk_ioctl() context only.

We could add a safety check in ipmr_ioctl() at the risk of breaking
applications.

Instead, remove sk_is_ipmr() and sk_is_icmpv6() because their
name would be misleading, once we change their implementation.

[1]
BUG: KASAN: stack-out-of-bounds in ipmr_ioctl+0xb12/0xbd0 net/ipv4/ipmr.c:1654
Read of size 4 at addr ffffc90003aefae4 by task syz-executor105/5004

CPU: 0 PID: 5004 Comm: syz-executor105 Not tainted 6.4.0-rc6-syzkaller-01304-gc08afcdc #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/27/2023
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xd9/0x150 lib/dump_stack.c:106
print_address_description.constprop.0+0x2c/0x3c0 mm/kasan/report.c:351
print_report mm/kasan/report.c:462 [inline]
kasan_report+0x11c/0x130 mm/kasan/report.c:572
ipmr_ioctl+0xb12/0xbd0 net/ipv4/ipmr.c:1654
raw_ioctl+0x4e/0x1e0 net/ipv4/raw.c:881
sock_ioctl_out net/core/sock.c:4186 [inline]
sk_ioctl+0x151/0x440 net/core/sock.c:4214
inet_ioctl+0x18c/0x380 net/ipv4/af_inet.c:1001
sock_do_ioctl+0xcc/0x230 net/socket.c:1189
sock_ioctl+0x1f8/0x680 net/socket.c:1306
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]
__se_sys_ioctl fs/ioctl.c:856 [inline]
__x64_sys_ioctl+0x197/0x210 fs/ioctl.c:856
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f2944bf6ad9
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:00007ffd8897a028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f2944bf6ad9
RDX: 0000000000000000 RSI: 00000000000089e1 RDI: 0000000000000003
RBP: 00007f2944bbac80 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f2944bbad10
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
</TASK>

The buggy address belongs to stack of task syz-executor105/5004
and is located at offset 36 in frame:
sk_ioctl+0x0/0x440 net/core/sock.c:4172

This frame has 2 objects:
[32, 36) 'karg'
[48, 88) 'buffer'

Fixes: e1d001fa ("net: ioctl: Use kernel memory on protocol ioctl callbacks")
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Breno Leitao <leitao@debian.org>
Cc: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/20230619124336.651528-1-edumazet@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>