From: Jeff Hostetler <jeffhost@xxxxxxxxxxxxx>
Update `unix_stream_listen()` to take an options structure to override
default behaviors. This includes the size of the `listen()` backlog
and whether it should always unlink the socket file before trying to
create a new one. Also eliminate calls to `die()` if it cannot create
a socket.
Normally, `unix_stream_listen()` always tries to `unlink()` the
socket-path before calling `bind()`. If there is an existing
server/daemon already bound and listening on that socket-path, our
`unlink()` would have the effect of disassociating the existing
server's bound-socket-fd from the socket-path without notifying the
existing server. The existing server could continue to service
existing connections (accepted-socket-fd's), but would not receive any
futher new connections (since clients rendezvous via the socket-path).
The existing server would effectively be offline but yet appear to be
active.
Furthermore, `unix_stream_listen()` creates an opportunity for a brief
race condition for connecting clients if they try to connect in the
interval between the forced `unlink()` and the subsequent `bind()` (which
recreates the socket-path that is bound to a new socket-fd in the current
process).
Signed-off-by: Jeff Hostetler <jeffhost@xxxxxxxxxxxxx>
---
builtin/credential-cache--daemon.c | 3 ++-
unix-socket.c | 28 +++++++++++++++++++++-------
unix-socket.h | 14 +++++++++++++-
3 files changed, 36 insertions(+), 9 deletions(-)
diff --git a/builtin/credential-cache--daemon.c b/builtin/credential-cache--daemon.c
index c61f123a3b8..4c6c89ab0de 100644
--- a/builtin/credential-cache--daemon.c
+++ b/builtin/credential-cache--daemon.c
@@ -203,9 +203,10 @@ static int serve_cache_loop(int fd)
static void serve_cache(const char *socket_path, int debug)
{
+ struct unix_stream_listen_opts opts = UNIX_STREAM_LISTEN_OPTS_INIT;
int fd;
- fd = unix_stream_listen(socket_path);
+ fd = unix_stream_listen(socket_path, &opts);
if (fd < 0)
die_errno("unable to bind to '%s'", socket_path);
diff --git a/unix-socket.c b/unix-socket.c
index ef2aeb46bcd..8bcef18ea55 100644
--- a/unix-socket.c
+++ b/unix-socket.c
@@ -88,24 +88,35 @@ int unix_stream_connect(const char *path)
return -1;
}
-int unix_stream_listen(const char *path)
+int unix_stream_listen(const char *path,
+ const struct unix_stream_listen_opts *opts)
{
- int fd, saved_errno;
+ int fd = -1;
+ int saved_errno;
+ int bind_successful = 0;
+ int backlog;
struct sockaddr_un sa;
struct unix_sockaddr_context ctx;
- unlink(path);
-
if (unix_sockaddr_init(&sa, path, &ctx) < 0)
return -1;
+
fd = socket(AF_UNIX, SOCK_STREAM, 0);
if (fd < 0)
- die_errno("unable to create socket");
+ goto fail;
+
+ if (opts->force_unlink_before_bind)
+ unlink(path);
if (bind(fd, (struct sockaddr *)&sa, sizeof(sa)) < 0)
goto fail;
+ bind_successful = 1;
- if (listen(fd, 5) < 0)
+ if (opts->listen_backlog_size > 0)
+ backlog = opts->listen_backlog_size;
+ else
+ backlog = 5;
+ if (listen(fd, backlog) < 0)
goto fail;
unix_sockaddr_cleanup(&ctx);
@@ -114,7 +125,10 @@ int unix_stream_listen(const char *path)
fail:
saved_errno = errno;
unix_sockaddr_cleanup(&ctx);
- close(fd);
+ if (fd != -1)
+ close(fd);
+ if (bind_successful)
+ unlink(path);
errno = saved_errno;
return -1;
}
diff --git a/unix-socket.h b/unix-socket.h
index e271aeec5a0..c28372ef48e 100644
--- a/unix-socket.h
+++ b/unix-socket.h
@@ -1,7 +1,19 @@
#ifndef UNIX_SOCKET_H
#define UNIX_SOCKET_H
+struct unix_stream_listen_opts {
+ int listen_backlog_size;
+ unsigned int force_unlink_before_bind:1;
+};
+
+#define UNIX_STREAM_LISTEN_OPTS_INIT \
+{ \
+ .listen_backlog_size = 5, \
+ .force_unlink_before_bind = 1, \
+}
+
int unix_stream_connect(const char *path);
-int unix_stream_listen(const char *path);
+int unix_stream_listen(const char *path,
+ const struct unix_stream_listen_opts *opts);
#endif /* UNIX_SOCKET_H */
--
gitgitgadget
