From 2fa91ee391b7bbed960bf404a405573c64d836aa Mon Sep 17 00:00:00 2001 From: David Gibson Date: Wed, 17 Jul 2024 10:36:04 +1000 Subject: udp: Handle errors on UDP sockets Currently we ignore all events other than EPOLLIN on UDP sockets. This means that if we ever receive an EPOLLERR event, we'll enter an infinite loop on epoll, because we'll never do anything to clear the error. Luckily that doesn't seem to have happened in practice, but it's certainly fragile. Furthermore changes in how we handle UDP sockets with the flow table mean we will start receiving error events. Add handling of EPOLLERR events. For now we just read the error from the error queue (thereby clearing the error state) and print a debug message. We can add more substantial handling of specific events in future if we want to. Signed-off-by: David Gibson Signed-off-by: Stefano Brivio --- udp.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 60 insertions(+) (limited to 'udp.c') diff --git a/udp.c b/udp.c index fbf3ce7..150f970 100644 --- a/udp.c +++ b/udp.c @@ -110,6 +110,7 @@ #include #include #include +#include #include "checksum.h" #include "util.h" @@ -728,6 +729,59 @@ static void udp_tap_prepare(const struct ctx *c, const struct mmsghdr *mmh, (*tap_iov)[UDP_IOV_PAYLOAD].iov_len = l4len; } +/** + * udp_sock_recverr() - Receive and clear an error from a socket + * @s: Socket to receive from + * + * Return: true if errors received and processed, false if no more errors + * + * #syscalls recvmsg + */ +static bool udp_sock_recverr(int s) +{ + const struct sock_extended_err *ee; + const struct cmsghdr *hdr; + char buf[CMSG_SPACE(sizeof(*ee))]; + struct msghdr mh = { + .msg_name = NULL, + .msg_namelen = 0, + .msg_iov = NULL, + .msg_iovlen = 0, + .msg_control = buf, + .msg_controllen = sizeof(buf), + }; + ssize_t rc; + + rc = recvmsg(s, &mh, MSG_ERRQUEUE); + if (rc < 0) { + if (errno != EAGAIN && errno != EWOULDBLOCK) + err_perror("Failed to read error queue"); + return false; + } + + if (!(mh.msg_flags & MSG_ERRQUEUE)) { + err("Missing MSG_ERRQUEUE flag reading error queue"); + return false; + } + + hdr = CMSG_FIRSTHDR(&mh); + if (!((hdr->cmsg_level == IPPROTO_IP && + hdr->cmsg_type == IP_RECVERR) || + (hdr->cmsg_level == IPPROTO_IPV6 && + hdr->cmsg_type == IPV6_RECVERR))) { + err("Unexpected cmsg reading error queue"); + return false; + } + + ee = (const struct sock_extended_err *)CMSG_DATA(hdr); + + /* TODO: When possible propagate and otherwise handle errors */ + debug("%s error on UDP socket %i: %s", + str_ee_origin(ee), s, strerror(ee->ee_errno)); + + return true; +} + /** * udp_sock_recv() - Receive datagrams from a socket * @c: Execution context @@ -751,6 +805,12 @@ static int udp_sock_recv(const struct ctx *c, int s, uint32_t events, ASSERT(!c->no_udp); + /* Clear any errors first */ + if (events & EPOLLERR) { + while (udp_sock_recverr(s)) + ; + } + if (!(events & EPOLLIN)) return 0; -- cgit v1.2.3