(cherry-pick) Don't call getsockname(2) in Tcl_MakeFileChannel(3) unless absolutely necessary. Closes RFE [0ac9d06895]. Permits better constraining of Tcl/tclsh via OpenBSD's pledge(2) or similar mechanisms. Minor rewrite

1 files changed, 9 insertions, 7 deletions

diff --git a/unix/tclUnixChan.c b/unix/tclUnixChan.c
index 0957282..132f690 100644
--- a/unix/tclUnixChan.c
+++ b/unix/tclUnixChan.c
@@ -1975,27 +1975,29 @@ Tcl_MakeFileChannel(
     char channelName[16 + TCL_INTEGER_SPACE];
     int fd = PTR2INT(handle);
     const Tcl_ChannelType *channelTypePtr;
-    struct sockaddr sockaddr;
-    socklen_t sockaddrLen = sizeof(sockaddr);
+    Tcl_StatBuf buf;
 
     if (mode == 0) {
 	return NULL;
     }
 
-    sockaddr.sa_family = AF_UNSPEC;
-
 #ifdef SUPPORTS_TTY
     if (isatty(fd)) {
 	channelTypePtr = &ttyChannelType;
 	snprintf(channelName, sizeof(channelName), "serial%d", fd);
     } else
 #endif /* SUPPORTS_TTY */
-    if ((getsockname(fd, (struct sockaddr *)&sockaddr, &sockaddrLen) == 0)
+    if (TclOSfstat(fd, &buf) == 0 && S_ISSOCK(buf.st_mode)) {
+	struct sockaddr sockaddr;
+	socklen_t sockaddrLen = sizeof(sockaddr);
+
+	sockaddr.sa_family = AF_UNSPEC;
+	if ((getsockname(fd, (struct sockaddr *)&sockaddr, &sockaddrLen) == 0)
 		&& (sockaddrLen > 0)
 		&& (sockaddr.sa_family == AF_INET
 			|| sockaddr.sa_family == AF_INET6)) {
-	return (Tcl_Channel)TclpMakeTcpClientChannelMode(INT2PTR(fd), mode);
-    } else {
+	    return (Tcl_Channel)TclpMakeTcpClientChannelMode(INT2PTR(fd), mode);
+	}
 	channelTypePtr = &fileChannelType;
 	snprintf(channelName, sizeof(channelName), "file%d", fd);
     }