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rtnetlink: Remove VLA usage
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In the quest to remove all stack VLA usage from the kernel[1], this
allocates the maximum size expected for all possible types and adds
sanity-checks at both registration and usage to make sure nothing gets
out of sync. This matches the proposed VLA solution for nfnetlink[2]. The
values chosen here were based on finding assignments for .maxtype and
.slave_maxtype and manually counting the enums:

slave_maxtype (max 33):
	IFLA_BRPORT_MAX     33
	IFLA_BOND_SLAVE_MAX  9

maxtype (max 45):
	IFLA_BOND_MAX       28
	IFLA_BR_MAX         45
	__IFLA_CAIF_HSI_MAX  8
	IFLA_CAIF_MAX        4
	IFLA_CAN_MAX        16
	IFLA_GENEVE_MAX     12
	IFLA_GRE_MAX        25
	IFLA_GTP_MAX         5
	IFLA_HSR_MAX         7
	IFLA_IPOIB_MAX       4
	IFLA_IPTUN_MAX      21
	IFLA_IPVLAN_MAX      3
	IFLA_MACSEC_MAX     15
	IFLA_MACVLAN_MAX     7
	IFLA_PPP_MAX         2
	__IFLA_RMNET_MAX     4
	IFLA_VLAN_MAX        6
	IFLA_VRF_MAX         2
	IFLA_VTI_MAX         7
	IFLA_VXLAN_MAX      28
	VETH_INFO_MAX        2
	VXCAN_INFO_MAX       2

This additionally changes maxtype and slave_maxtype fields to unsigned,
since they're only ever using positive values.

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
[2] https://patchwork.kernel.org/patch/10439647/

Signed-off-by: Kees Cook <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
Signed-off-by: Oktapra Amtono <[email protected]>
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kees authored and radcolor committed Nov 28, 2020
1 parent 513445d commit ea08052
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Showing 2 changed files with 18 additions and 4 deletions.
4 changes: 2 additions & 2 deletions include/net/rtnetlink.h
Original file line number Diff line number Diff line change
Expand Up @@ -56,7 +56,7 @@ struct rtnl_link_ops {
size_t priv_size;
void (*setup)(struct net_device *dev);

int maxtype;
unsigned int maxtype;
const struct nla_policy *policy;
int (*validate)(struct nlattr *tb[],
struct nlattr *data[]);
Expand All @@ -81,7 +81,7 @@ struct rtnl_link_ops {
unsigned int (*get_num_tx_queues)(void);
unsigned int (*get_num_rx_queues)(void);

int slave_maxtype;
unsigned int slave_maxtype;
const struct nla_policy *slave_policy;
int (*slave_validate)(struct nlattr *tb[],
struct nlattr *data[]);
Expand Down
18 changes: 16 additions & 2 deletions net/core/rtnetlink.c
Original file line number Diff line number Diff line change
Expand Up @@ -57,6 +57,9 @@
#include <net/rtnetlink.h>
#include <net/net_namespace.h>

#define RTNL_MAX_TYPE 48
#define RTNL_SLAVE_MAX_TYPE 36

struct rtnl_link {
rtnl_doit_func doit;
rtnl_dumpit_func dumpit;
Expand Down Expand Up @@ -326,6 +329,11 @@ int rtnl_link_register(struct rtnl_link_ops *ops)
{
int err;

/* Sanity-check max sizes to avoid stack buffer overflow. */
if (WARN_ON(ops->maxtype > RTNL_MAX_TYPE ||
ops->slave_maxtype > RTNL_SLAVE_MAX_TYPE))
return -EINVAL;

rtnl_lock();
err = __rtnl_link_register(ops);
rtnl_unlock();
Expand Down Expand Up @@ -2258,13 +2266,16 @@ static int rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh)
}

if (1) {
struct nlattr *attr[ops ? ops->maxtype + 1 : 1];
struct nlattr *slave_attr[m_ops ? m_ops->slave_maxtype + 1 : 1];
struct nlattr *attr[RTNL_MAX_TYPE + 1];
struct nlattr *slave_attr[RTNL_SLAVE_MAX_TYPE + 1];
struct nlattr **data = NULL;
struct nlattr **slave_data = NULL;
struct net *dest_net, *link_net = NULL;

if (ops) {
if (ops->maxtype > RTNL_MAX_TYPE)
return -EINVAL;

if (ops->maxtype && linkinfo[IFLA_INFO_DATA]) {
err = nla_parse_nested(attr, ops->maxtype,
linkinfo[IFLA_INFO_DATA],
Expand All @@ -2281,6 +2292,9 @@ static int rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh)
}

if (m_ops) {
if (ops->slave_maxtype > RTNL_SLAVE_MAX_TYPE)
return -EINVAL;

if (m_ops->slave_maxtype &&
linkinfo[IFLA_INFO_SLAVE_DATA]) {
err = nla_parse_nested(slave_attr,
Expand Down

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