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Emulated Netlink sockets cause infinite busy loops under event-loop #112

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63 changes: 56 additions & 7 deletions src/syscall/netlink.c
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,7 @@
#include "syscall/abi.h"
#include "syscall/internal.h"
#include "syscall/net.h"
#include "utils.h"

static void netlink_close(int guest_fd);

Expand Down Expand Up @@ -130,6 +131,7 @@ typedef struct {
size_t buf_pos; /* Current read position */
uint32_t seq; /* Sequence number from last request */
uint32_t pid; /* Bound PID (from bind or auto-assigned) */
int pipe_wr; /* Host pipe write descriptor */
} netlink_state_t;

static netlink_state_t nl_state[MAX_NETLINK_FDS];
Expand All @@ -156,6 +158,7 @@ static netlink_state_t *nl_alloc(int guest_fd)
memset(s, 0, sizeof(*s));
s->in_use = true;
s->guest_fd = guest_fd;
s->pipe_wr = -1;
s->buf = malloc(NETLINK_BUF_SIZE);
if (!s->buf) {
s->in_use = false;
Expand All @@ -167,6 +170,26 @@ static netlink_state_t *nl_alloc(int guest_fd)
return NULL;
}

static void netlink_signal_readable(netlink_state_t *ns)
{
if (ns->pipe_wr != -1) {
uint8_t dummy = 1;
(void) write(ns->pipe_wr, &dummy, 1);
}
}

static void netlink_clear_readable(int guest_fd)
{
int host_fd = fd_to_host(guest_fd);
if (host_fd < 0)
return;

uint8_t dummy[128];
while (read(host_fd, dummy, sizeof(dummy)) > 0) {
/* Drain non-blocking pipe */
}
}

/* Append a netlink attribute to the buffer. Returns bytes written. */
static size_t nl_put_attr(uint8_t *buf,
size_t max,
Expand Down Expand Up @@ -423,6 +446,12 @@ int64_t netlink_socket(int protocol, int type)
if (pipe(pipefd) < 0)
return -LINUX_EMFILE;

if (fd_set_nonblock(pipefd[0]) < 0 || fd_set_nonblock(pipefd[1]) < 0) {
close(pipefd[0]);
close(pipefd[1]);
return -LINUX_EMFILE;
}

int gfd = fd_alloc(FD_NETLINK, pipefd[0], netlink_close);
if (gfd < 0) {
close(pipefd[0]);
Expand All @@ -438,10 +467,7 @@ int64_t netlink_socket(int protocol, int type)
return -LINUX_ENOMEM;
}

/* No poll wakeup fd is needed because recvmsg drains the buffered response
* directly.
*/
close(pipefd[1]); /* The write end is unused */
ns->pipe_wr = pipefd[1];

return gfd;
}
Expand Down Expand Up @@ -605,6 +631,9 @@ int64_t netlink_sendmsg(int guest_fd, guest_t *g, uint64_t msg_gva, int flags)
}

int ret = nl_process_request(ns, req, rlen);
if (ret == 0) {
netlink_signal_readable(ns);
}
result = (ret < 0) ? ret : (int64_t) iov.iov_len;

out:
Expand Down Expand Up @@ -636,6 +665,9 @@ int64_t netlink_send(int guest_fd, guest_t *g, uint64_t buf_gva, uint64_t len)
}

int ret = nl_process_request(ns, req, rlen);
if (ret == 0) {
netlink_signal_readable(ns);
}
result = (ret < 0) ? ret : (int64_t) len;

out:
Expand All @@ -662,7 +694,7 @@ int64_t netlink_recv(int guest_fd,

if (ns->buf_pos >= ns->buf_len) {
pthread_mutex_unlock(&nl_lock);
return 0;
return -LINUX_EAGAIN;
}

size_t avail = ns->buf_len - ns->buf_pos;
Expand All @@ -689,6 +721,10 @@ int64_t netlink_recv(int guest_fd,
}
ns->buf_pos += msg_end;

if (ns->buf_pos >= ns->buf_len) {
netlink_clear_readable(guest_fd);
}

if (src_gva && addrlen_gva) {
sockaddr_nl_t snl = {
.nl_family = LINUX_AF_NETLINK,
Expand Down Expand Up @@ -748,7 +784,7 @@ int64_t netlink_recvmsg(int guest_fd, guest_t *g, uint64_t msg_gva, int flags)

if (ns->buf_pos >= ns->buf_len) {
pthread_mutex_unlock(&nl_lock);
return 0;
return -LINUX_EAGAIN;
}

/* Parse msghdr to get iovec */
Expand Down Expand Up @@ -804,6 +840,10 @@ int64_t netlink_recvmsg(int guest_fd, guest_t *g, uint64_t msg_gva, int flags)

ns->buf_pos += msg_end;

if (ns->buf_pos >= ns->buf_len) {
netlink_clear_readable(guest_fd);
}

/* Write back sockaddr_nl if caller provided msg_name */
if (mhdr.msg_name && mhdr.msg_namelen >= sizeof(sockaddr_nl_t)) {
sockaddr_nl_t snl = {
Expand Down Expand Up @@ -839,7 +879,7 @@ int64_t netlink_read(int guest_fd, guest_t *g, uint64_t buf_gva, uint64_t count)

if (ns->buf_pos >= ns->buf_len) {
pthread_mutex_unlock(&nl_lock);
return 0;
return -LINUX_EAGAIN;
}

size_t avail = ns->buf_len - ns->buf_pos;
Expand All @@ -851,6 +891,11 @@ int64_t netlink_read(int guest_fd, guest_t *g, uint64_t buf_gva, uint64_t count)
}

ns->buf_pos += to_copy;

if (ns->buf_pos >= ns->buf_len) {
netlink_clear_readable(guest_fd);
}

pthread_mutex_unlock(&nl_lock);
return (int64_t) to_copy;
}
Expand All @@ -863,6 +908,10 @@ static void netlink_close(int guest_fd)
pthread_mutex_unlock(&nl_lock);
return;
}
if (ns->pipe_wr != -1) {
close(ns->pipe_wr);
ns->pipe_wr = -1;
}
free(ns->buf);
ns->buf = NULL;
ns->in_use = false;
Expand Down
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