net: dcb: choose correct policy to parse DCB_ATTR_BCN

The dcbnl_bcn_setcfg uses erroneous policy to parse tb[DCB_ATTR_BCN],
which is introduced in commit 859ee3c ("DCB: Add support for DCB
BCN"). Please see the comment in below code

static int dcbnl_bcn_setcfg(...)
{
  ...
  ret = nla_parse_nested_deprecated(..., dcbnl_pfc_up_nest, .. )
  // !!! dcbnl_pfc_up_nest for attributes
  //  DCB_PFC_UP_ATTR_0 to DCB_PFC_UP_ATTR_ALL in enum dcbnl_pfc_up_attrs
  ...
  for (i = DCB_BCN_ATTR_RP_0; i <= DCB_BCN_ATTR_RP_7; i++) {
  // !!! DCB_BCN_ATTR_RP_0 to DCB_BCN_ATTR_RP_7 in enum dcbnl_bcn_attrs
    ...
    value_byte = nla_get_u8(data[i]);
    ...
  }
  ...
  for (i = DCB_BCN_ATTR_BCNA_0; i <= DCB_BCN_ATTR_RI; i++) {
  // !!! DCB_BCN_ATTR_BCNA_0 to DCB_BCN_ATTR_RI in enum dcbnl_bcn_attrs
  ...
    value_int = nla_get_u32(data[i]);
  ...
  }
  ...
}

That is, the nla_parse_nested_deprecated uses dcbnl_pfc_up_nest
attributes to parse nlattr defined in dcbnl_pfc_up_attrs. But the
following access code fetch each nlattr as dcbnl_bcn_attrs attributes.
By looking up the associated nla_policy for dcbnl_bcn_attrs. We can find
the beginning part of these two policies are "same".

static const struct nla_policy dcbnl_pfc_up_nest[...] = {
        [DCB_PFC_UP_ATTR_0]   = {.type = NLA_U8},
        [DCB_PFC_UP_ATTR_1]   = {.type = NLA_U8},
        [DCB_PFC_UP_ATTR_2]   = {.type = NLA_U8},
        [DCB_PFC_UP_ATTR_3]   = {.type = NLA_U8},
        [DCB_PFC_UP_ATTR_4]   = {.type = NLA_U8},
        [DCB_PFC_UP_ATTR_5]   = {.type = NLA_U8},
        [DCB_PFC_UP_ATTR_6]   = {.type = NLA_U8},
        [DCB_PFC_UP_ATTR_7]   = {.type = NLA_U8},
        [DCB_PFC_UP_ATTR_ALL] = {.type = NLA_FLAG},
};

static const struct nla_policy dcbnl_bcn_nest[...] = {
        [DCB_BCN_ATTR_RP_0]         = {.type = NLA_U8},
        [DCB_BCN_ATTR_RP_1]         = {.type = NLA_U8},
        [DCB_BCN_ATTR_RP_2]         = {.type = NLA_U8},
        [DCB_BCN_ATTR_RP_3]         = {.type = NLA_U8},
        [DCB_BCN_ATTR_RP_4]         = {.type = NLA_U8},
        [DCB_BCN_ATTR_RP_5]         = {.type = NLA_U8},
        [DCB_BCN_ATTR_RP_6]         = {.type = NLA_U8},
        [DCB_BCN_ATTR_RP_7]         = {.type = NLA_U8},
        [DCB_BCN_ATTR_RP_ALL]       = {.type = NLA_FLAG},
        // from here is somewhat different
        [DCB_BCN_ATTR_BCNA_0]       = {.type = NLA_U32},
        ...
        [DCB_BCN_ATTR_ALL]          = {.type = NLA_FLAG},
};

Therefore, the current code is buggy and this
nla_parse_nested_deprecated could overflow the dcbnl_pfc_up_nest and use
the adjacent nla_policy to parse attributes from DCB_BCN_ATTR_BCNA_0.

Hence use the correct policy dcbnl_bcn_nest to parse the nested
tb[DCB_ATTR_BCN] TLV.

Fixes: 859ee3c ("DCB: Add support for DCB BCN")
Signed-off-by: Lin Ma <linma@zju.edu.cn>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20230801013248.87240-1-linma@zju.edu.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: f0rm2l1n

net/dcb/dcbnl.c

@@ -980,7 +980,7 @@ static int dcbnl_bcn_setcfg(struct net_device *netdev, struct nlmsghdr *nlh,
 		return -EOPNOTSUPP;
 
 	ret = nla_parse_nested_deprecated(data, DCB_BCN_ATTR_MAX,
-					  tb[DCB_ATTR_BCN], dcbnl_pfc_up_nest,
+					  tb[DCB_ATTR_BCN], dcbnl_bcn_nest,
 					  NULL);
 	if (ret)
 		return ret;