Issue

Symptom/Problem

• SIGSEGV occurs when customer use an editor with a console screen of bterm

Environment

• Red Hat Enterprise Linux 5.3 i386

Resolution

• There are a patch proposed against this issue. Fixed in Red Hat Enterprise Linux 5.3 Fastrack channel.

• Refer to the patch below:

  diff -up bogl-0.1.18/bogl-term.c.original bogl-0.1.18/bogl-term.c
  --- bogl-0.1.18/bogl-term.c.original     2009-08-17 23:43:22.000000000 +0900
  +++ bogl-0.1.18/bogl-term.c     2009-08-17 23:44:11.000000000 +0900
  @@ -465,6 +465,7 @@ bogl_term_out (struct bogl_term *term, c
                       /* Move all other lines down.  Fortunately, this is easy.  */
                       dirty_backscroll(term);
                       term->yorig--;
  +                    if(term->yorig==-1) term->yorig=term->ysize-1;
  
                       /* Clear the top line.  */
                       for (i = SCR (0, 0); i < SCR (term->xsize, 0); i++)
  

Diagnostic Steps (internal)

• Reproducer:

  • boot with kernel option vga=771

  • start vi to edit 80 lines of file

  • shift + g to reach bottom

  • continuously press k to move cursor up.

  • just about the next line to the top-most line, SEGV occurs.

• backtrace:

  #0  bogl_term_out (term=0x855c9e0, 
  s=0xbfc81670 "\033[1;1Hline 39\r\033[?25h\033[2J\033[1;1Hline 40\r\nline 41\r\nline 42\r\nline 43\r\nline 44\r\nline 45\r\nline 46\r\nline 47\r\nline 48\r\nline 49\r\nline 50\r\nline 51\r\nline 52\r\nline 53\r\nline 54\r\nline 55\r\nline 56\r\nline 57\r\nline 58\r"..., n=20) at bogl-term.c:472
  

Root Cause

• term->yorig is invalid. It crashes when the value is negative.
• under bterm scrolling by a line is no problem, whereas it's not adopting well to jump, i.e. :80 (jump to 80th line), ctrl+f, ctrl+g etc. It does not update term->yorig. After these jumps going back by line decrements term->yorig, which eventually reaches -1, resulting in segv.

Comments (internal)

• The trace shows:

  308 void309 bogl_term_out (struct bogl_term *term, char *s, int n)310 {
  469                     /* Clear the top line.  */
  470                     for (i = SCR (0, 0); i < SCR (term->xsize, 0); i++)
  471                     {
  472                         term->screen[i] = ' '; ###<---
  473                         term->screenfg[i] = term->fg;
  474                         term->screenbg[i] = term->bg;
  475                         term->screenul[i] = 0;
  476                         term->cchars[i] = 0;
  477                         term->dirty[i] = 1;
  478                     }
  479                 }
  480             }
  

• Actually this occurs when doing SCR macro:

  96 #define SCR(x, y) \
  97 ((x) + (((y) + term->yorig) % term->ysize) * term->xsize)
  

• yorig being negative number:

(gdb) p *term
     $2 = {font = 0x20, xbase = 32, ybase = 32, xsize = 32, ysize = 32, xstep = 32, ystep = 32, xpos = 32,
       ypos = 32, def_fg = 32, def_bg = 32, fg = 32, bg = 32, ul = 32, rev = 32, state = 32, cur_visible = 32,
       xp = 32, yp = 32, arg = {32, 32}, ps = {flags_ = 32, wcout_ = 32}, screen = 0x20, screenfg = 0x8562800,
       screenbg = 0x85672d8, screenul = 0x856bdb0, dirty = 0x8561548 "\001", cchars = 0x8570888, yorig = -1,
       acs = 0, utf = "M\000\000\000\000", utfn = 0}

Comments (external)

*