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udp: Fix breakage of UDP error handling by PKTINFO support

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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 for received datagrams")
Reported-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
David Gibson 2025-04-15 17:16:18 +10:00 • committed by Stefano Brivio
parent 50249086a9
commit baf049f8e0
1 changed files with 17 additions and 13 deletions

30
udp.c
View file

@ -155,6 +155,10 @@ __attribute__ ((aligned(32)))
#endif #endif
udp_meta[UDP_MAX_FRAMES]; 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 * enum udp_iov_idx - Indices for the buffers making up a single UDP frame
* @UDP_IOV_TAP tap specific header * @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; struct sock_extended_err ee;
union sockaddr_inany saddr; union sockaddr_inany saddr;
}; };
const struct errhdr *eh; char buf[PKTINFO_SPACE + CMSG_SPACE(sizeof(struct errhdr))];
const struct cmsghdr *hdr;
char buf[CMSG_SPACE(sizeof(struct errhdr))];
char data[ICMP6_MAX_DLEN]; char data[ICMP6_MAX_DLEN];
const struct errhdr *eh;
struct cmsghdr *hdr;
int s = ref.fd; int s = ref.fd;
struct iovec iov = { struct iovec iov = {
.iov_base = data, .iov_base = data,
@ -507,12 +511,16 @@ static int udp_sock_recverr(const struct ctx *c, union epoll_ref ref)
return -1; return -1;
} }
hdr = CMSG_FIRSTHDR(&mh); for (hdr = CMSG_FIRSTHDR(&mh); hdr; hdr = CMSG_NXTHDR(&mh, hdr)) {
if (!((hdr->cmsg_level == IPPROTO_IP && if ((hdr->cmsg_level == IPPROTO_IP &&
hdr->cmsg_type == IP_RECVERR) || hdr->cmsg_type == IP_RECVERR) ||
(hdr->cmsg_level == IPPROTO_IPV6 && (hdr->cmsg_level == IPPROTO_IPV6 &&
hdr->cmsg_type == IPV6_RECVERR))) { hdr->cmsg_type == IPV6_RECVERR))
err("Unexpected cmsg reading error queue"); break;
}
if (!hdr) {
err("Missing RECVERR cmsg in error queue");
return -1; return -1;
} }
@ -587,10 +595,6 @@ static int udp_sock_errs(const struct ctx *c, union epoll_ref ref)
return n_err; 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 * udp_peek_addr() - Get source address for next packet
* @s: Socket to get information from * @s: Socket to get information from