qemu-ga: obey LISTEN_PID when using systemd socket activation

qemu-ga's socket activation support was not obeying the LISTEN_PID
environment variable, which avoids that a process uses a socket-activation
file descriptor meant for its parent.

Mess can for example ensue if a process forks a children before consuming
the socket-activation file descriptor and therefore setting O_CLOEXEC
on it.

Luckily, qemu-nbd also got socket activation code, and its copy does
support LISTEN_PID.  Some extra fixups are needed to ensure that the
code can be used for both, but that's what this patch does.  The
main change is to replace get_listen_fds's "consume" argument with
the FIRST_SOCKET_ACTIVATION_FD macro from the qemu-nbd code.

Cc: "Richard W.M. Jones" <rjones@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Daniel P. Berrange <berrange@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 8 insertions, 92 deletions

diff --git a/qemu-nbd.c b/qemu-nbd.c
index e4fede6..e080fb7 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -28,6 +28,7 @@
 #include "qemu/config-file.h"
 #include "qemu/bswap.h"
 #include "qemu/log.h"
+#include "qemu/systemd.h"
 #include "block/snapshot.h"
 #include "qapi/util.h"
 #include "qapi/qmp/qstring.h"
@@ -474,98 +475,6 @@ static void setup_address_and_port(const char **address, const char **port)
     }
 }
 
-#define FIRST_SOCKET_ACTIVATION_FD 3 /* defined by systemd ABI */
-
-#ifndef _WIN32
-/*
- * Check if socket activation was requested via use of the
- * LISTEN_FDS and LISTEN_PID environment variables.
- *
- * Returns 0 if no socket activation, or the number of FDs.
- */
-static unsigned int check_socket_activation(void)
-{
-    const char *s;
-    unsigned long pid;
-    unsigned long nr_fds;
-    unsigned int i;
-    int fd;
-    int err;
-
-    s = getenv("LISTEN_PID");
-    if (s == NULL) {
-        return 0;
-    }
-    err = qemu_strtoul(s, NULL, 10, &pid);
-    if (err) {
-        if (verbose) {
-            fprintf(stderr, "malformed %s environment variable (ignored)\n",
-                    "LISTEN_PID");
-        }
-        return 0;
-    }
-    if (pid != getpid()) {
-        if (verbose) {
-            fprintf(stderr, "%s was not for us (ignored)\n",
-                    "LISTEN_PID");
-        }
-        return 0;
-    }
-
-    s = getenv("LISTEN_FDS");
-    if (s == NULL) {
-        return 0;
-    }
-    err = qemu_strtoul(s, NULL, 10, &nr_fds);
-    if (err) {
-        if (verbose) {
-            fprintf(stderr, "malformed %s environment variable (ignored)\n",
-                    "LISTEN_FDS");
-        }
-        return 0;
-    }
-    assert(nr_fds <= UINT_MAX);
-
-    /* A limitation of current qemu-nbd is that it can only listen on
-     * a single socket.  When that limitation is lifted, we can change
-     * this function to allow LISTEN_FDS > 1, and remove the assertion
-     * in the main function below.
-     */
-    if (nr_fds > 1) {
-        error_report("qemu-nbd does not support socket activation with %s > 1",
-                     "LISTEN_FDS");
-        exit(EXIT_FAILURE);
-    }
-
-    /* So these are not passed to any child processes we might start. */
-    unsetenv("LISTEN_FDS");
-    unsetenv("LISTEN_PID");
-
-    /* So the file descriptors don't leak into child processes. */
-    for (i = 0; i < nr_fds; ++i) {
-        fd = FIRST_SOCKET_ACTIVATION_FD + i;
-        if (fcntl(fd, F_SETFD, FD_CLOEXEC) == -1) {
-            /* If we cannot set FD_CLOEXEC then it probably means the file
-             * descriptor is invalid, so socket activation has gone wrong
-             * and we should exit.
-             */
-            error_report("Socket activation failed: "
-                         "invalid file descriptor fd = %d: %m",
-                         fd);
-            exit(EXIT_FAILURE);
-        }
-    }
-
-    return (unsigned int) nr_fds;
-}
-
-#else /* !_WIN32 */
-static unsigned int check_socket_activation(void)
-{
-    return 0;
-}
-#endif
-
 /*
  * Check socket parameters compatibility when socket activation is used.
  */
@@ -892,6 +801,13 @@ int main(int argc, char **argv)
             error_report("%s", err_msg);
             exit(EXIT_FAILURE);
         }
+
+        /* qemu-nbd can only listen on a single socket.  */
+        if (socket_activation > 1) {
+            error_report("qemu-nbd does not support socket activation with %s > 1",
+                         "LISTEN_FDS");
+            exit(EXIT_FAILURE);
+        }
     }
 
     if (tlscredsid) {