net: dcb: choose correct policy to parse DCB_ATTR_BCN

In the Linux kernel, the following vulnerability has been resolved:

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 859ee3c43812 ("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.