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  1. Guacamole
  2. GUACAMOLE-149

Potential busy loop in guac_terminal_display_set_columns()

    Details

      Description

      The Guacamole terminal emulator can get caught in an endless busy loop if a character in the buffer ends up being set with zero width. The loop within guac_terminal_display_set_columns() advances through columns by the width of the current character, and will never advance if that width is somehow unset.

      (gdb) bt
      #0  guac_terminal_display_set_columns (display=0x30f5480, row=11, start_column=22, end_column=22, character=0x2cf3b18)
          at display.c:458
      #1  0x00007f8b3fa68374 in guac_terminal_commit_cursor (term=term@entry=0x2c0b5b0) at terminal.c:649
      #2  0x00007f8b3fa69329 in guac_terminal_flush (terminal=terminal@entry=0x2c0b5b0) at terminal.c:1339
      #3  0x00007f8b3fa69440 in guac_terminal_render_frame (terminal=0x2c0b5b0) at terminal.c:489
      #4  0x000000000040312d in __guacd_client_output_thread (data=0x2bea930) at client.c:73
      #5  0x00007f8b43469184 in start_thread (arg=0x7f8b3c326700) at pthread_create.c:312
      #6  0x00007f8b4319637d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111
      (gdb) f 0
      #0  guac_terminal_display_set_columns (display=0x30f5480, row=11, start_column=22, end_column=22, character=0x2cf3b18)
          at display.c:458
      458             current->type      = GUAC_CHAR_SET;
      (gdb) list
      453
      454         /* For each column in range */
      455         for (i = start_column; i <= end_column; i += character->width) {
      456
      457             /* Set operation */
      458             current->type      = GUAC_CHAR_SET;
      459             current->character = *character;
      460
      461             /* Next character */
      462             current += character->width;
      (gdb) p character->width
      $113 = 0
      (gdb)
      

      From __guac_terminal_set(), it's clear that having zero width is a legitimate value:

          /* Calculate width in columns */
          width = wcwidth(codepoint);
          if (width < 0)
              width = 1;
      
          /* Do nothing if glyph is empty */
          if (width == 0)
              return 0;
      

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          • Assignee:
            mike.jumper Michael Jumper
            Reporter:
            aiden0z Aiden Luo
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            Dates

            • Created:
              Updated:
              Resolved:

              Development