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authorJohannes Berg <johannes.berg@intel.com>2020-04-30 22:13:06 +0200
committerDavid S. Miller <davem@davemloft.net>2020-04-30 17:51:41 -0700
commit7690aa1cdf7c4565ad6b013b324c28b685505e24 (patch)
treeb033fd6f80a1eb1972935660663321c1168c7f59 /lib
parent47a1494b8208461094923400c396ce4b8163c064 (diff)
downloadlwn-7690aa1cdf7c4565ad6b013b324c28b685505e24.tar.gz
lwn-7690aa1cdf7c4565ad6b013b324c28b685505e24.zip
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>
Diffstat (limited to 'lib')
-rw-r--r--lib/nlattr.c46
1 files changed, 34 insertions, 12 deletions
diff --git a/lib/nlattr.c b/lib/nlattr.c
index 3df05db732ca..7f7ebd89caa4 100644
--- a/lib/nlattr.c
+++ b/lib/nlattr.c
@@ -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);