From 7690aa1cdf7c4565ad6b013b324c28b685505e24 Mon Sep 17 00:00:00 2001 From: Johannes Berg Date: Thu, 30 Apr 2020 22:13:06 +0200 Subject: 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 Signed-off-by: David S. Miller --- lib/nlattr.c | 46 ++++++++++++++++++++++++++++++++++------------ 1 file changed, 34 insertions(+), 12 deletions(-) (limited to 'lib/nlattr.c') 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); -- cgit v1.2.3