Fix arbitrary command execution in ed-style patches (CVE-2018-1000156)

* src/pch.c (do_ed_script): Write ed script to a temporary file instead
of piping it to ed: this will cause ed to abort on invalid commands
instead of rejecting them and carrying on.
* tests/ed-style: New test case.
* tests/Makefile.am (TESTS): Add test case.

src/pch.c

@@ -33,6 +33,7 @@
 # include <io.h>
 #endif
 #include <safe.h>
+#include <sys/wait.h>
 
 #define INITHUNKMAX 125			/* initial dynamic allocation size */
 
@@ -2389,24 +2390,28 @@ do_ed_script (char const *inname, char const *outname,
     static char const editor_program[] = EDITOR_PROGRAM;
 
     file_offset beginning_of_this_line;
-    FILE *pipefp = 0;
     size_t chars_read;
+    FILE *tmpfp = 0;
+    char const *tmpname;
+    int tmpfd;
+    pid_t pid;
+
+    if (! dry_run && ! skip_rest_of_patch)
+      {
+	/* Write ed script to a temporary file.  This causes ed to abort on
+	   invalid commands such as when line numbers or ranges exceed the
+	   number of available lines.  When ed reads from a pipe, it rejects
+	   invalid commands and treats the next line as a new command, which
+	   can lead to arbitrary command execution.  */
+
+	tmpfd = make_tempfile (&tmpname, 'e', NULL, O_RDWR | O_BINARY, 0);
+	if (tmpfd == -1)
+	  pfatal ("Can't create temporary file %s", quotearg (tmpname));
+	tmpfp = fdopen (tmpfd, "w+b");
+	if (! tmpfp)
+	  pfatal ("Can't open stream for file %s", quotearg (tmpname));
+      }
 
-    if (! dry_run && ! skip_rest_of_patch) {
-	int exclusive = *outname_needs_removal ? 0 : O_EXCL;
-	if (inerrno != ENOENT)
-	  {
-	    *outname_needs_removal = true;
-	    copy_file (inname, outname, 0, exclusive, instat.st_mode, true);
-	  }
-	sprintf (buf, "%s %s%s", editor_program,
-		 verbosity == VERBOSE ? "" : "- ",
-		 outname);
-	fflush (stdout);
-	pipefp = popen(buf, binary_transput ? "wb" : "w");
-	if (!pipefp)
-	  pfatal ("Can't open pipe to %s", quotearg (buf));
-    }
     for (;;) {
 	char ed_command_letter;
 	beginning_of_this_line = file_tell (pfp);
@@ -2417,14 +2422,14 @@ do_ed_script (char const *inname, char const *outname,
 	}
 	ed_command_letter = get_ed_command_letter (buf);
 	if (ed_command_letter) {
-	    if (pipefp)
-		if (! fwrite (buf, sizeof *buf, chars_read, pipefp))
+	    if (tmpfp)
+		if (! fwrite (buf, sizeof *buf, chars_read, tmpfp))
 		    write_fatal ();
 	    if (ed_command_letter != 'd' && ed_command_letter != 's') {
 	        p_pass_comments_through = true;
 		while ((chars_read = get_line ()) != 0) {
-		    if (pipefp)
-			if (! fwrite (buf, sizeof *buf, chars_read, pipefp))
+		    if (tmpfp)
+			if (! fwrite (buf, sizeof *buf, chars_read, tmpfp))
 			    write_fatal ();
 		    if (chars_read == 2  &&  strEQ (buf, ".\n"))
 			break;
@@ -2437,13 +2442,49 @@ do_ed_script (char const *inname, char const *outname,
 	    break;
 	}
     }
-    if (!pipefp)
+    if (!tmpfp)
       return;
-    if (fwrite ("w\nq\n", sizeof (char), (size_t) 4, pipefp) == 0
-	|| fflush (pipefp) != 0)
+    if (fwrite ("w\nq\n", sizeof (char), (size_t) 4, tmpfp) == 0
+	|| fflush (tmpfp) != 0)
       write_fatal ();
-    if (pclose (pipefp) != 0)
-      fatal ("%s FAILED", editor_program);
+
+    if (lseek (tmpfd, 0, SEEK_SET) == -1)
+      pfatal ("Can't rewind to the beginning of file %s", quotearg (tmpname));
+
+    if (! dry_run && ! skip_rest_of_patch) {
+	int exclusive = *outname_needs_removal ? 0 : O_EXCL;
+	*outname_needs_removal = true;
+	if (inerrno != ENOENT)
+	  {
+	    *outname_needs_removal = true;
+	    copy_file (inname, outname, 0, exclusive, instat.st_mode, true);
+	  }
+	sprintf (buf, "%s %s%s", editor_program,
+		 verbosity == VERBOSE ? "" : "- ",
+		 outname);
+	fflush (stdout);
+
+	pid = fork();
+	if (pid == -1)
+	  pfatal ("Can't fork");
+	else if (pid == 0)
+	  {
+	    dup2 (tmpfd, 0);
+	    execl ("/bin/sh", "sh", "-c", buf, (char *) 0);
+	    _exit (2);
+	  }
+	else
+	  {
+	    int wstatus;
+	    if (waitpid (pid, &wstatus, 0) == -1
+	        || ! WIFEXITED (wstatus)
+		|| WEXITSTATUS (wstatus) != 0)
+	      fatal ("%s FAILED", editor_program);
+	  }
+    }
+
+    fclose (tmpfp);
+    safe_unlink (tmpname);
 
     if (ofp)
       {

tests/Makefile.am

@@ -32,6 +32,7 @@ TESTS = \
 	crlf-handling \
 	dash-o-append \
 	deep-directories \
+	ed-style \
 	empty-files \
 	false-match \
 	fifo \

tests/ed-style

@@ -0,0 +1,41 @@
+# Copyright (C) 2018 Free Software Foundation, Inc.
+#
+# Copying and distribution of this file, with or without modification,
+# in any medium, are permitted without royalty provided the copyright
+# notice and this notice are preserved.
+
+. $srcdir/test-lib.sh
+
+require cat
+use_local_patch
+use_tmpdir
+
+# ==============================================================
+
+cat > ed1.diff <<EOF
+0a
+foo
+.
+EOF
+
+check 'patch -e foo -i ed1.diff' <<EOF
+EOF
+
+check 'cat foo' <<EOF
+foo
+EOF
+
+cat > ed2.diff <<EOF
+1337a
+r !echo bar
+,p
+EOF
+
+check 'patch -e foo -i ed2.diff 2> /dev/null || echo "Status: $?"' <<EOF
+?
+Status: 2
+EOF
+
+check 'cat foo' <<EOF
+foo
+EOF