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net: handle multi-part netlink responses

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Handle multi-part netlink responses to prevent truncated results from
large routing tables.

Previously, we only made a single recv call, which led to incomplete
results when the kernel split the message into multiple responses (which
happens frequently with NLM_F_DUMP).

Also guard against a potential hanging issue where the code would
indefinitely wait for NLMSG_DONE for non-multi-part responses by
detecting the NLM_F_MULTI flag and only continue waiting when necessary.
This commit is contained in:
willcl-ark
2025-04-01 14:15:50 +01:00
committed by will
parent 42e99ad773
commit 88db09bafe
1 changed files with 59 additions and 37 deletions
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24
src/common/netif.cpp
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@@ -36,6 +36,9 @@ namespace {
// will fail, so we skip that. // will fail, so we skip that.
#if defined(__linux__) || (defined(__FreeBSD__) && __FreeBSD_version >= 1400000) #if defined(__linux__) || (defined(__FreeBSD__) && __FreeBSD_version >= 1400000)
// Good for responses containing ~ 10,000-15,000 routes.
static constexpr ssize_t NETLINK_MAX_RESPONSE_SIZE{1'048'576};
std::optional<CNetAddr> QueryDefaultGatewayImpl(sa_family_t family) std::optional<CNetAddr> QueryDefaultGatewayImpl(sa_family_t family)
{ {
// Create a netlink socket. // Create a netlink socket.
@@ -84,6 +87,9 @@ std::optional<CNetAddr> QueryDefaultGatewayImpl(sa_family_t family)
// Receive response. // Receive response.
char response[4096]; char response[4096];
ssize_t total_bytes_read{0};
bool done{false};
while (!done) {
int64_t recv_result; int64_t recv_result;
do { do {
recv_result = sock->Recv(response, sizeof(response), 0); recv_result = sock->Recv(response, sizeof(response), 0);
@@ -93,7 +99,22 @@ std::optional<CNetAddr> QueryDefaultGatewayImpl(sa_family_t family)
return std::nullopt; return std::nullopt;
} }
total_bytes_read += recv_result;
if (total_bytes_read > NETLINK_MAX_RESPONSE_SIZE) {
LogPrintLevel(BCLog::NET, BCLog::Level::Warning, "Netlink response exceeded size limit (%zu bytes, family=%d)\n", NETLINK_MAX_RESPONSE_SIZE, family);
return std::nullopt;
}
for (nlmsghdr* hdr = (nlmsghdr*)response; NLMSG_OK(hdr, recv_result); hdr = NLMSG_NEXT(hdr, recv_result)) { for (nlmsghdr* hdr = (nlmsghdr*)response; NLMSG_OK(hdr, recv_result); hdr = NLMSG_NEXT(hdr, recv_result)) {
if (!(hdr->nlmsg_flags & NLM_F_MULTI)) {
done = true;
}
if (hdr->nlmsg_type == NLMSG_DONE) {
done = true;
break;
}
rtmsg* r = (rtmsg*)NLMSG_DATA(hdr); rtmsg* r = (rtmsg*)NLMSG_DATA(hdr);
int remaining_len = RTM_PAYLOAD(hdr); int remaining_len = RTM_PAYLOAD(hdr);
@@ -107,7 +128,7 @@ std::optional<CNetAddr> QueryDefaultGatewayImpl(sa_family_t family)
} }
// Iterate over the attributes. // Iterate over the attributes.
rtattr *rta_gateway = nullptr; rtattr* rta_gateway = nullptr;
int scope_id = 0; int scope_id = 0;
for (rtattr* attr = RTM_RTA(r); RTA_OK(attr, remaining_len); attr = RTA_NEXT(attr, remaining_len)) { for (rtattr* attr = RTM_RTA(r); RTA_OK(attr, remaining_len); attr = RTA_NEXT(attr, remaining_len)) {
if (attr->rta_type == RTA_GATEWAY) { if (attr->rta_type == RTA_GATEWAY) {
@@ -130,6 +151,7 @@ std::optional<CNetAddr> QueryDefaultGatewayImpl(sa_family_t family)
} }
} }
} }
}
return std::nullopt; return std::nullopt;
} }