files: allocate enough space for the prompt when finding a lock file

Instead of allocating a fixed amount of 128 bytes, which will overflow
and segfault, adjust the allocation to the length of the file name, and
if necessary trim the file name to make the prompt fit on the screen.

This fixes https://savannah.gnu.org/bugs/?47511

.
Reported-by: Aapo Rantalainen <aapo.rantalainen@gmail.com>
Signed-off-by: Benno Schulenberg <bensberg@justemail.net>

src/files.c

@@ -310,8 +310,8 @@ int delete_lockfile(const char *lockfilename)
  * complain to the user. */
 int do_lockfile(const char *filename)
 {
-    char *namecopy1 = (char *) mallocstrcpy(NULL, filename);
-    char *namecopy2 = (char *) mallocstrcpy(NULL, filename);
+    char *namecopy = (char *) mallocstrcpy(NULL, filename);
+    char *secondcopy = (char *) mallocstrcpy(NULL, filename);
     size_t locknamesize = strlen(filename) + strlen(locking_prefix)
 		+ strlen(locking_suffix) + 3;
     char *lockfilename = charalloc(locknamesize);
@@ -319,18 +319,17 @@ int do_lockfile(const char *filename)
     struct stat fileinfo;
     int lockfd, lockpid, retval = -1;
 
-    snprintf(lockfilename, locknamesize, "%s/%s%s%s", dirname(namecopy1),
-		locking_prefix, basename(namecopy2), locking_suffix);
-    free(namecopy1);
-    free(namecopy2);
+    snprintf(lockfilename, locknamesize, "%s/%s%s%s", dirname(namecopy),
+		locking_prefix, basename(secondcopy), locking_suffix);
+    free(secondcopy);
 #ifdef DEBUG
     fprintf(stderr, "lock file name is %s\n", lockfilename);
 #endif
     if (stat(lockfilename, &fileinfo) != -1) {
 	ssize_t readtot = 0;
 	ssize_t readamt = 0;
-	char *lockbuf, *promptstr;
-	int ans;
+	char *lockbuf, *question, *promptstr;
+	int room, ans;
 
 	if ((lockfd = open(lockfilename, O_RDONLY)) < 0) {
 	    statusbar(_("Error opening lock file %s: %s"),
@@ -361,10 +360,19 @@ int do_lockfile(const char *filename)
 	fprintf(stderr, "program name which created this lock file should be %s\n", lockprog);
 	fprintf(stderr, "user which created this lock file should be %s\n", lockuser);
 #endif
-	promptstr = charalloc(128);
 	/* TRANSLATORS: The second %s is the name of the user, the third that of the editor. */
-	sprintf(promptstr, _("File %s is being edited (by %s with %s, PID %d); continue?"),
-			filename, lockuser, lockprog, lockpid);
+	question = _("File %s is being edited (by %s with %s, PID %d); continue?");
+	room = COLS - strlenpt(question) - strlenpt(lockuser) - strlenpt(lockprog) + 3;
+	if (room < 4)
+	    namecopy = mallocstrcpy(namecopy, "_");
+	else if (room < strlenpt(filename))
+	    sprintf(namecopy, "...%s", display_string(filename,
+				strlenpt(filename) - room + 3, room, FALSE));
+
+	/* Allow extra space for username (14), program name (8), PID (3),
+	 * and terminating \0 (1), minus the %s (2) for the file name. */
+	promptstr = charalloc(strlen(question) + 24 + strlen(namecopy));
+	sprintf(promptstr, question, namecopy, lockuser, lockprog, lockpid);
 	ans = do_yesno_prompt(FALSE, promptstr);
 	free(promptstr);
 
@@ -377,6 +385,7 @@ int do_lockfile(const char *filename)
     retval = write_lockfile(lockfilename, filename, FALSE);
 
   free_the_name:
+    free(namecopy);
     if (retval < 1)
 	free(lockfilename);