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netlink: limit recursion depth in policy validation 

Now that we have nested policies, we can theoretically
recurse forever parsing attributes if a (sub-)policy
refers back to a higher level one. This is a situation
that has happened in nl80211, and we've avoided it there
by not linking it.

Add some code to netlink parsing to limit recursion depth.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Johannes Berg 2020-04-30 22:13:06 +02:00 committed by David S. Miller
parent 47a1494b82
commit 7690aa1cdf
1 changed files with 34 additions and 12 deletions
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46
lib/nlattr.c
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@ -44,6 +44,20 @@ static const u8 nla_attr_minlen[NLA_TYPE_MAX+1] = {
[NLA_S64] = sizeof(s64),
};
/*
* Nested policies might refer back to the original
* policy in some cases, and userspace could try to
* abuse that and recurse by nesting in the right
* ways. Limit recursion to avoid this problem.
*/
#define MAX_POLICY_RECURSION_DEPTH 10
static int __nla_validate_parse(const struct nlattr *head, int len, int maxtype,
const struct nla_policy *policy,
unsigned int validate,
struct netlink_ext_ack *extack,
struct nlattr **tb, unsigned int depth);
static int validate_nla_bitfield32(const struct nlattr *nla,
const u32 valid_flags_mask)
{
@ -70,7 +84,7 @@ static int validate_nla_bitfield32(const struct nlattr *nla,
static int nla_validate_array(const struct nlattr *head, int len, int maxtype,
const struct nla_policy *policy,
struct netlink_ext_ack *extack,
unsigned int validate)
unsigned int validate, unsigned int depth)
{
const struct nlattr *entry;
int rem;
@ -87,8 +101,9 @@ static int nla_validate_array(const struct nlattr *head, int len, int maxtype,
return -ERANGE;
}
ret = __nla_validate(nla_data(entry), nla_len(entry),
maxtype, policy, validate, extack);
ret = __nla_validate_parse(nla_data(entry), nla_len(entry),
maxtype, policy, validate, extack,
NULL, depth + 1);
if (ret < 0)
return ret;
}
@ -156,7 +171,7 @@ static int nla_validate_int_range(const struct nla_policy *pt,
static int validate_nla(const struct nlattr *nla, int maxtype,
const struct nla_policy *policy, unsigned int validate,
struct netlink_ext_ack *extack)
struct netlink_ext_ack *extack, unsigned int depth)
{
u16 strict_start_type = policy[0].strict_start_type;
const struct nla_policy *pt;
@ -269,9 +284,10 @@ static int validate_nla(const struct nlattr *nla, int maxtype,
if (attrlen < NLA_HDRLEN)
goto out_err;
if (pt->nested_policy) {
err = __nla_validate(nla_data(nla), nla_len(nla), pt->len,
pt->nested_policy, validate,
extack);
err = __nla_validate_parse(nla_data(nla), nla_len(nla),
pt->len, pt->nested_policy,
validate, extack, NULL,
depth + 1);
if (err < 0) {
/*
* return directly to preserve the inner
@ -294,7 +310,7 @@ static int validate_nla(const struct nlattr *nla, int maxtype,
err = nla_validate_array(nla_data(nla), nla_len(nla),
pt->len, pt->nested_policy,
extack, validate);
extack, validate, depth);
if (err < 0) {
/*
* return directly to preserve the inner
@ -358,11 +374,17 @@ static int __nla_validate_parse(const struct nlattr *head, int len, int maxtype,
const struct nla_policy *policy,
unsigned int validate,
struct netlink_ext_ack *extack,
struct nlattr **tb)
struct nlattr **tb, unsigned int depth)
{
const struct nlattr *nla;
int rem;
if (depth >= MAX_POLICY_RECURSION_DEPTH) {
NL_SET_ERR_MSG(extack,
"allowed policy recursion depth exceeded");
return -EINVAL;
}
if (tb)
memset(tb, 0, sizeof(struct nlattr *) * (maxtype + 1));
@ -379,7 +401,7 @@ static int __nla_validate_parse(const struct nlattr *head, int len, int maxtype,
}
if (policy) {
int err = validate_nla(nla, maxtype, policy,
validate, extack);
validate, extack, depth);
if (err < 0)
return err;
@ -421,7 +443,7 @@ int __nla_validate(const struct nlattr *head, int len, int maxtype,
struct netlink_ext_ack *extack)
{
return __nla_validate_parse(head, len, maxtype, policy, validate,
extack, NULL);
extack, NULL, 0);
}
EXPORT_SYMBOL(__nla_validate);
@ -476,7 +498,7 @@ int __nla_parse(struct nlattr **tb, int maxtype,
struct netlink_ext_ack *extack)
{
return __nla_validate_parse(head, len, maxtype, policy, validate,
extack, tb);
extack, tb, 0);
}
EXPORT_SYMBOL(__nla_parse);