netlabel: fix out-of-bounds memory accesses

In calipso_map_cat_ntoh(), in the for loop, if the return value of
netlbl_bitmap_walk() is equal to (net_clen_bits - 1), when
netlbl_bitmap_walk() is called next time, out-of-bounds memory accesses
of bitmap[byte_offset] occurs.

The bug was found during fuzzing. The following is the fuzzing report
 BUG: KASAN: slab-out-of-bounds in netlbl_bitmap_walk+0x3c/0xd0
 Read of size 1 at addr ffffff8107bf6f70 by task err_OH/252

 CPU: 7 PID: 252 Comm: err_OH Not tainted 5.17.0-rc7+ #17
 Hardware name: linux,dummy-virt (DT)
 Call trace:
  dump_backtrace+0x21c/0x230
  show_stack+0x1c/0x60
  dump_stack_lvl+0x64/0x7c
  print_address_description.constprop.0+0x70/0x2d0
  __kasan_report+0x158/0x16c
  kasan_report+0x74/0x120
  __asan_load1+0x80/0xa0
  netlbl_bitmap_walk+0x3c/0xd0
  calipso_opt_getattr+0x1a8/0x230
  calipso_sock_getattr+0x218/0x340
  calipso_sock_getattr+0x44/0x60
  netlbl_sock_getattr+0x44/0x80
  selinux_netlbl_socket_setsockopt+0x138/0x170
  selinux_socket_setsockopt+0x4c/0x60
  security_socket_setsockopt+0x4c/0x90
  __sys_setsockopt+0xbc/0x2b0
  __arm64_sys_setsockopt+0x6c/0x84
  invoke_syscall+0x64/0x190
  el0_svc_common.constprop.0+0x88/0x200
  do_el0_svc+0x88/0xa0
  el0_svc+0x128/0x1b0
  el0t_64_sync_handler+0x9c/0x120
  el0t_64_sync+0x16c/0x170
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wang Yufen <wangyufen@huawei.com>
Acked-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/netlabel/netlabel_kapi.c

@@ -885,6 +885,8 @@ int netlbl_bitmap_walk(const unsigned char *bitmap, u32 bitmap_len,
 	unsigned char bitmask;
 	unsigned char byte;
 
+	if (offset >= bitmap_len)
+		return -1;
 	byte_offset = offset / 8;
 	byte = bitmap[byte_offset];
 	bit_spot = offset;