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fix potential race condition in DefaultResolver when discard_cache() #698

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fix potential race condition in DefaultResolver when discard_cache() #698

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13 changes: 5 additions & 8 deletions net/utils.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -260,17 +260,12 @@ class DefaultResolver : public Resolver {
IPAddr addr;
IPAddrNode(IPAddr addr) : addr(addr) {}
};
using IPAddrList = intrusive_list<IPAddrNode>;
struct IPAddrList : public intrusive_list<IPAddrNode>, rwlock {
~IPAddrList() { delete_all(); }
};
public:
DefaultResolver(uint64_t cache_ttl, uint64_t resolve_timeout)
: dnscache_(cache_ttl), resolve_timeout_(resolve_timeout) {}
~DefaultResolver() {
for (auto it : dnscache_) {
((IPAddrList*)it->_obj)->delete_all();
}
dnscache_.clear();
}

IPAddr resolve(const char *host) override {
auto ctr = [&]() -> IPAddrList* {
auto addrs = new IPAddrList();
Expand All @@ -295,6 +290,7 @@ class DefaultResolver : public Resolver {
};
auto ips = dnscache_.borrow(host, ctr);
if (ips->empty()) LOG_ERRNO_RETURN(0, IPAddr(), "Domain resolution for ` failed", host);
scoped_rwlock _(*ips, RLOCK);
auto ret = ips->front();
ips->node = ret->next(); // access in round robin order
return ret->addr;
Expand All @@ -304,6 +300,7 @@ class DefaultResolver : public Resolver {

void discard_cache(const char *host, IPAddr ip) override {
auto ipaddr = dnscache_.borrow(host);
scoped_rwlock _(*ipaddr, WLOCK);
if (ip.undefined() || ipaddr->empty()) {
ipaddr->delete_all();
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recycle will destruct ipaddrlist so do not need to delete items right here, and also do not need a write lock in such condition.

ipaddr.recycle(true);
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