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epoll: Always use epoll_ref for the epoll data variable

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epoll_ref contains a variety of information useful when handling epoll
events on our sockets, and we place it in the epoll_event data field
returned by epoll.  However, for a few other things we use the 'fd' field
in the standard union of types for that data field.

This actually introduces a bug which is vanishingly unlikely to hit in
practice, but very nasty if it ever did: theoretically if we had a very
large file descriptor number for fd_tap or fd_tap_listen it could overflow
into bits that overlap with the 'proto' field in epoll_ref.  With some
very bad luck this could mean that we mistakenly think an event on a
regular socket is an event on fd_tap or fd_tap_listen.

More practically, using different (but overlapping) fields of the
epoll_data means we can't unify dispatch for the various different objects
in the epoll.  Therefore use the same epoll_ref as the data for the tap
fds and the netns quit fd, adding new fd type values to describe them.

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 2023-08-11 15:12:22 +10:00 committed by Stefano Brivio
parent 3401644453
commit 6a6735ece4
4 changed files with 29 additions and 12 deletions
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11
passt.c
View file

@ -60,6 +60,8 @@ char *epoll_type_str[EPOLL_TYPE_MAX + 1] = {
[EPOLL_TYPE_UDP] = "UDP socket",
[EPOLL_TYPE_ICMP] = "ICMP socket",
[EPOLL_TYPE_ICMPV6] = "ICMPv6 socket",
[EPOLL_TYPE_NSQUIT] = "namespace inotify",
[EPOLL_TYPE_TAP] = "tap device",
};
/**
@ -328,12 +330,11 @@ loop:
for (i = 0; i < nfds; i++) {
union epoll_ref ref = *((union epoll_ref *)&events[i].data.u64);
int fd = events[i].data.fd;
if (fd == c.fd_tap || fd == c.fd_tap_listen)
tap_handler(&c, fd, events[i].events, &now);
else if (fd == quit_fd)
pasta_netns_quit_handler(&c, fd);
if (ref.type == EPOLL_TYPE_TAP)
tap_handler(&c, ref.fd, events[i].events, &now);
else if (ref.type == EPOLL_TYPE_NSQUIT)
pasta_netns_quit_handler(&c, quit_fd);
else
sock_handler(&c, ref, events[i].events, &now);
}

6
passt.h
View file

@ -55,8 +55,12 @@ enum epoll_type {
EPOLL_TYPE_ICMP,
/* ICMPv6 sockets */
EPOLL_TYPE_ICMPV6,
/* inotify fd watching for end of netns (pasta) */
EPOLL_TYPE_NSQUIT,
/* tap char device, or qemu socket fd */
EPOLL_TYPE_TAP,
EPOLL_TYPE_MAX = EPOLL_TYPE_ICMPV6,
EPOLL_TYPE_MAX = EPOLL_TYPE_TAP,
};
/**

8
pasta.c
View file

@ -365,7 +365,10 @@ void pasta_ns_conf(struct ctx *c)
int pasta_netns_quit_init(struct ctx *c)
{
int flags = O_NONBLOCK | O_CLOEXEC;
struct epoll_event ev = { .events = EPOLLIN };
union epoll_ref ref = { .type = EPOLL_TYPE_NSQUIT };
struct epoll_event ev = {
.events = EPOLLIN
};
int inotify_fd;
if (c->mode != MODE_PASTA || c->no_netns_quit || !*c->netns_base)
@ -381,7 +384,8 @@ int pasta_netns_quit_init(struct ctx *c)
return -1;
}
ev.data.fd = inotify_fd;
ref.fd = inotify_fd;
ev.data.u64 = ref.u64;
epoll_ctl(c->epollfd, EPOLL_CTL_ADD, inotify_fd, &ev);
return inotify_fd;

16
tap.c
View file

@ -1071,6 +1071,7 @@ restart:
static void tap_sock_unix_init(struct ctx *c)
{
int fd = socket(AF_UNIX, SOCK_STREAM, 0);
union epoll_ref ref = { .type = EPOLL_TYPE_TAP };
struct epoll_event ev = { 0 };
struct sockaddr_un addr = {
.sun_family = AF_UNIX,
@ -1123,8 +1124,9 @@ static void tap_sock_unix_init(struct ctx *c)
listen(fd, 0);
ev.data.fd = c->fd_tap_listen = fd;
ref.fd = c->fd_tap_listen = fd;
ev.events = EPOLLIN | EPOLLET;
ev.data.u64 = ref.u64;
epoll_ctl(c->epollfd, EPOLL_CTL_ADD, c->fd_tap_listen, &ev);
info("You can now start qemu (>= 7.2, with commit 13c6be96618c):");
@ -1141,6 +1143,7 @@ static void tap_sock_unix_init(struct ctx *c)
*/
static void tap_sock_unix_new(struct ctx *c, uint32_t events)
{
union epoll_ref ref = { .type = EPOLL_TYPE_TAP };
struct epoll_event ev = { 0 };
int v = INT_MAX / 2;
struct ucred ucred;
@ -1180,8 +1183,9 @@ static void tap_sock_unix_new(struct ctx *c, uint32_t events)
setsockopt(c->fd_tap, SOL_SOCKET, SO_SNDBUF, &v, sizeof(v)))
trace("tap: failed to set SO_SNDBUF to %i", v);
ev.data.fd = c->fd_tap;
ref.fd = c->fd_tap;
ev.events = EPOLLIN | EPOLLET | EPOLLRDHUP;
ev.data.u64 = ref.u64;
epoll_ctl(c->epollfd, EPOLL_CTL_ADD, c->fd_tap, &ev);
}
@ -1226,6 +1230,7 @@ static int tap_ns_tun(void *arg)
*/
static void tap_sock_tun_init(struct ctx *c)
{
union epoll_ref ref = { .type = EPOLL_TYPE_TAP };
struct epoll_event ev = { 0 };
NS_CALL(tap_ns_tun, c);
@ -1234,8 +1239,9 @@ static void tap_sock_tun_init(struct ctx *c)
pasta_ns_conf(c);
ev.data.fd = c->fd_tap;
ref.fd = c->fd_tap;
ev.events = EPOLLIN | EPOLLRDHUP;
ev.data.u64 = ref.u64;
epoll_ctl(c->epollfd, EPOLL_CTL_ADD, c->fd_tap, &ev);
}
@ -1257,11 +1263,13 @@ void tap_sock_init(struct ctx *c)
}
if (c->fd_tap != -1) { /* Passed as --fd */
union epoll_ref ref = { .type = EPOLL_TYPE_TAP };
struct epoll_event ev = { 0 };
ASSERT(c->one_off);
ev.data.fd = c->fd_tap;
ref.fd = c->fd_tap;
ev.events = EPOLLIN | EPOLLET | EPOLLRDHUP;
ev.data.u64 = ref.u64;
epoll_ctl(c->epollfd, EPOLL_CTL_ADD, c->fd_tap, &ev);
return;
}