fix: harden the per-user IPC endpoint

bench/main.c

@@ -4,8 +4,6 @@
 #include <string.h>
 #include <unistd.h>
 #include <time.h>
-#include <sys/socket.h>
-#include <sys/un.h>
 #include "../ipc.h"
 
 typedef struct Key Key;
@@ -81,15 +79,8 @@ loadkeys(char *file)
 static void
 dial(void)
 {
-	struct sockaddr_un addr;
-
-	fd = socket(AF_UNIX, SOCK_STREAM, 0);
+	fd = ipcconnect();
 	if(fd < 0)
-		die("socket");
-	memset(&addr, 0, sizeof(addr));
-	addr.sun_family = AF_UNIX;
-	snprintf(addr.sun_path, sizeof(addr.sun_path), IPCPATH, getuid());
-	if(connect(fd, (struct sockaddr*)&addr, sizeof(addr)) < 0)
 		die("connect");
 }
 

gtk/main.c

@@ -2,8 +2,6 @@
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
-#include <sys/socket.h>
-#include <sys/un.h>
 #include <gtk/gtk.h>
 #include "ipc.h"
 
@@ -27,20 +25,9 @@ static GType imtype;
 static void
 srvconnect(Im *im)
 {
-	struct sockaddr_un addr;
-
 	if(im->fd >= 0)
 		return;
-	im->fd = socket(AF_UNIX, SOCK_STREAM, 0);
-	if(im->fd < 0)
-		return;
-	memset(&addr, 0, sizeof(addr));
-	addr.sun_family = AF_UNIX;
-	snprintf(addr.sun_path, sizeof(addr.sun_path), IPCPATH, getuid());
-	if(connect(im->fd, (struct sockaddr*)&addr, sizeof(addr)) < 0){
-		close(im->fd);
-		im->fd = -1;
-	}
+	im->fd = ipcconnect();
 }
 
 static void

ipc.c

@@ -1,7 +1,10 @@
 #include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
 #include <sys/socket.h>
+#include <sys/un.h>
 #include "ipc.h"
 
 #if !defined(MSG_NOSIGNAL) && !defined(SO_NOSIGPIPE)
@@ -21,6 +24,49 @@ getlen(const unsigned char p[Ipclensz])
 	return p[0] | (p[1] << 8);
 }
 
+int
+ipcpath(char *dst, size_t cap)
+{
+	const char *dir, *sep;
+	int n;
+
+	if(dst == NULL || cap == 0)
+		return -1;
+	dir = getenv("XDG_RUNTIME_DIR");
+	if(dir != NULL && dir[0] == '/'){
+		sep = dir[strlen(dir)-1] == '/' ? "" : "/";
+		n = snprintf(dst, cap, "%s%sstrans.sock", dir, sep);
+	}else
+		n = snprintf(dst, cap, "/tmp/strans.%lu",
+			(unsigned long)getuid());
+	if(n < 0 || (size_t)n >= cap)
+		return -1;
+	return 0;
+}
+
+int
+ipcconnect(void)
+{
+	struct sockaddr_un addr;
+	int e, fd;
+
+	memset(&addr, 0, sizeof addr);
+	addr.sun_family = AF_UNIX;
+	if(ipcpath(addr.sun_path, sizeof addr.sun_path) < 0){
+		errno = ENAMETOOLONG;
+		return -1;
+	}
+	fd = socket(AF_UNIX, SOCK_STREAM, 0);
+	if(fd < 0)
+		return -1;
+	if(connect(fd, (struct sockaddr*)&addr, sizeof addr) == 0)
+		return fd;
+	e = errno;
+	close(fd);
+	errno = e;
+	return -1;
+}
+
 void
 ipcpackreq(unsigned char req[Ipcreqsz], int want, unsigned int mod,
 	unsigned int key)

ipc.h

@@ -3,8 +3,6 @@
 
 #include <stddef.h>
 
-#define IPCPATH "/tmp/strans.%d"
-
 /*
  * Request: [flags, modifiers, key byte 0, ..., key byte 3].
  * Flags request preedit and distinguish lifecycle reset from physical Escape.
@@ -61,5 +59,7 @@ int	ipcpackresp(unsigned char*, size_t, int, const char*, size_t, const char*, s
 int	ipcreadn(int, void*, size_t);
 int	ipcsend(int, const void*, size_t);
 int	ipcreadresp(int, int, char*, size_t, char*, size_t, Ipcresp*);
+int	ipcpath(char*, size_t);
+int	ipcconnect(void);
 
 #endif

srv.c

@@ -1,7 +1,10 @@
 #include "dat.h"
 #include "fn.h"
 
-static char adir[40];
+#include <sys/stat.h>
+#include <sys/un.h>
+
+static char adir[256];
 static Channel *clientc;
 
 typedef struct Client Client;
@@ -71,12 +74,16 @@ clientthread(void *arg)
 static void
 srvinit(void)
 {
-	char addr[64];
+	char addr[128], path[sizeof(((struct sockaddr_un*)0)->sun_path)];
 
-	snprint(addr, sizeof(addr), "unix!" IPCPATH, getuid());
-	remove(addr + 5);
+	if(ipcpath(path, sizeof path) < 0)
+		die("IPC path is too long");
+	if(snprint(addr, sizeof addr, "unix!%s", path) >= (int)sizeof addr)
+		die("IPC address is too long");
 	if(announce(addr, adir) < 0)
-		die("announce: %r");
+		die("IPC endpoint is already in use: %r");
+	if(chmod(path, 0600) < 0)
+		die("can't protect IPC endpoint: %s", path);
 }
 
 void

tests/ipc_test.c

@@ -1,3 +1,7 @@
+#define _POSIX_C_SOURCE 200809L
+
+#include <stdlib.h>
+#include <unistd.h>
 #include "test.h"
 
 void
@@ -21,3 +25,29 @@ ipc_masks_modifiers(struct ct *t)
 	CT_EQ_UINT(t, 0, key);
 	CT_CHECK(t, ipcreqreset(buf));
 }
+
+void
+ipc_runtime_path(struct ct *t)
+{
+	char buf[128], fallback[128], *old, *saved;
+
+	old = getenv("XDG_RUNTIME_DIR");
+	saved = old == nil ? nil : strdup(old);
+	setenv("XDG_RUNTIME_DIR", "/tmp/strans-runtime-test", 1);
+	CT_EQ_INT(t, 0, ipcpath(buf, sizeof buf));
+	CT_EQ_STR(t, "/tmp/strans-runtime-test/strans.sock", buf);
+	setenv("XDG_RUNTIME_DIR", "/tmp/strans-runtime-test/", 1);
+	CT_EQ_INT(t, 0, ipcpath(buf, sizeof buf));
+	CT_EQ_STR(t, "/tmp/strans-runtime-test/strans.sock", buf);
+	setenv("XDG_RUNTIME_DIR", "relative", 1);
+	CT_EQ_INT(t, 0, ipcpath(buf, sizeof buf));
+	snprint(fallback, sizeof fallback, "/tmp/strans.%d", getuid());
+	CT_EQ_STR(t, fallback, buf);
+	CT_EQ_INT(t, -1, ipcpath(buf, 4));
+	CT_EQ_INT(t, -1, ipcpath(nil, sizeof buf));
+	if(saved != nil){
+		setenv("XDG_RUNTIME_DIR", saved, 1);
+		free(saved);
+	}else
+		unsetenv("XDG_RUNTIME_DIR");
+}

tests/test.h

@@ -64,5 +64,6 @@ void	dictionary_candidates(struct ct*);
 void	dictionary_misses_clear_result(struct ct*);
 void	dictionary_emoji_identity(struct ct*);
 void	ipc_masks_modifiers(struct ct*);
+void	ipc_runtime_path(struct ct*);
 
 #endif

tests/unit_test.c

@@ -113,6 +113,7 @@ static const struct ct_test tests[] = {
 	{ "dict/misses-clear-result", dictionary_misses_clear_result },
 	{ "dict/emoji-identity", dictionary_emoji_identity },
 	{ "ipc/masks-modifiers", ipc_masks_modifiers },
+	{ "ipc/runtime-path", ipc_runtime_path },
 };
 
 void

xim/main.c

@@ -2,8 +2,6 @@
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
-#include <sys/socket.h>
-#include <sys/un.h>
 #include <xcb/xcb.h>
 #include <xkbcommon/xkbcommon.h>
 #include <xcb-imdkit/imdkit.h>
@@ -119,22 +117,11 @@ srvclose(Ic *state)
 static int
 srvconnect(Ic *state)
 {
-	struct sockaddr_un addr;
-	int fd;
-
 	if(state->fd >= 0)
 		return 0;
-	fd = socket(AF_UNIX, SOCK_STREAM, 0);
-	if(fd < 0)
+	state->fd = ipcconnect();
+	if(state->fd < 0)
 		return -1;
-	memset(&addr, 0, sizeof(addr));
-	addr.sun_family = AF_UNIX;
-	snprintf(addr.sun_path, sizeof(addr.sun_path), IPCPATH, getuid());
-	if(connect(fd, (struct sockaddr*)&addr, sizeof(addr)) < 0){
-		close(fd);
-		return -1;
-	}
-	state->fd = fd;
 	return 0;
 }