We recently enabled the IP_PKTINFO / IPV6_RECVPKTINFO socket options on our UDP sockets. This lets us obtain and properly handle the specific local address used when we're "listening" with a socket on 0.0.0.0 or ::. However, the PKTINFO cmsgs this option generates appear on error queue messages as well as regular datagrams. udp_sock_recverr() doesn't expect this and so flags an unrecoverable error when it can't parse the control message. Correct this by adding space in udp_sock_recverr()s control buffer for the additional PKTINFO data, and scan through all cmsgs for the RECVERR, rather than only looking at the first one. Link: https://bugs.passt.top/show_bug.cgi?id=99 Fixes: f4b0dd8b06 ("udp: Use PKTINFO cmsgs to get destination address..") Reported-by: Stefano Brivio <sbrivio(a)redhat.com> Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au> --- udp.c | 30 +++++++++++++++++------------- 1 file changed, 17 insertions(+), 13 deletions(-) diff --git a/udp.c b/udp.c index 40af7dfc..f5fb98c2 100644 --- a/udp.c +++ b/udp.c @@ -155,6 +155,10 @@ __attribute__ ((aligned(32))) #endif udp_meta[UDP_MAX_FRAMES]; +#define PKTINFO_SPACE \ + MAX(CMSG_SPACE(sizeof(struct in_pktinfo)), \ + CMSG_SPACE(sizeof(struct in6_pktinfo))) + /** * enum udp_iov_idx - Indices for the buffers making up a single UDP frame * @UDP_IOV_TAP tap specific header @@ -476,10 +480,10 @@ static int udp_sock_recverr(const struct ctx *c, union epoll_ref ref) struct sock_extended_err ee; union sockaddr_inany saddr; }; - const struct errhdr *eh; - const struct cmsghdr *hdr; - char buf[CMSG_SPACE(sizeof(struct errhdr))]; + char buf[PKTINFO_SPACE + CMSG_SPACE(sizeof(struct errhdr))]; char data[ICMP6_MAX_DLEN]; + const struct errhdr *eh; + struct cmsghdr *hdr; int s = ref.fd; struct iovec iov = { .iov_base = data, @@ -507,12 +511,16 @@ static int udp_sock_recverr(const struct ctx *c, union epoll_ref ref) return -1; } - 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"); + for (hdr = CMSG_FIRSTHDR(&mh); hdr; hdr = CMSG_NXTHDR(&mh, hdr)) { + if ((hdr->cmsg_level == IPPROTO_IP && + hdr->cmsg_type == IP_RECVERR) || + (hdr->cmsg_level == IPPROTO_IPV6 && + hdr->cmsg_type == IPV6_RECVERR)) + break; + } + + if (!hdr) { + err("Missing RECVERR cmsg in error queue"); return -1; } @@ -587,10 +595,6 @@ static int udp_sock_errs(const struct ctx *c, union epoll_ref ref) return n_err; } -#define PKTINFO_SPACE \ - MAX(CMSG_SPACE(sizeof(struct in_pktinfo)), \ - CMSG_SPACE(sizeof(struct in6_pktinfo))) - /** * udp_peek_addr() - Get source address for next packet * @s: Socket to get information from -- 2.49.0