Messages in this thread | | | Date | Thu, 25 May 2006 08:34:15 +0200 | From | Willy TARREAU <> | Subject | Re: uclinux 2.4.32 panic |
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On Wed, May 24, 2006 at 05:24:33PM -0400, Steve Clark wrote: (...) > >>>>LR; 008727cc <rs_write+148/294> > >> > >>>>PC; 0090e5fc <memmove+25c/460> <===== > >> > >>Trace; 0090e3a0 <memcpy+0/0> > >>Trace; 008727cc <rs_write+148/294> > >> > >>>>r8; 00956228 <tmp_buf+0/1000> > >> > >>Trace; 00872684 <rs_write+0/294> (...)
> The hardware is the ActionTec DualPC Modem it has a conexant cx82100 > arm processor. > I can reproduce it at will by connecting to the internet and running > nttcp thru it at the same time > I am scping file both ways from and to, and then finally starting a > getty on /dev/ttyS0, the modem is > at ttyS1 and also ttyS0 is where all the kernel printk messages come out. > > When I start the getty if I have all the other traffic going it > usually will panic in under a minute. IF I don't > have the getty running it will run for hours and not panic. > > > > 2.4.32-uc0 with patches from > http://www.bettina-attack.de/jonny/view.php/projects/uclinux_on_cx82100/
Well, at least the cnxtserial.c file looks suspicious to me :
static int rs_write(struct tty_struct * tty, int from_user, const unsigned char *buf, int count) { int c, total = 0; unsigned long flags; struct cnxt_serial *info = (struct cnxt_serial *)tty->driver_data; ^^^^^
if (serial_paranoia_check(info,tty->device, "rs_write")) ^^^^^ return 0;
if (!tty || !info->xmit_buf) return 0;
=> tty already referenced twice before the check. Either the check is useless, or the person who wrote it had a good reason for it which was not considered when writing the two lines above. I would suggest to start from something like this :
static int rs_write(struct tty_struct * tty, int from_user, const unsigned char *buf, int count) { int c, total = 0; unsigned long flags; struct cnxt_serial *info;
if (!tty) return 0;
info = (struct cnxt_serial *)tty->driver_data; if (serial_paranoia_check(info, tty->device, "rs_write")) return 0;
if (!info->xmit_buf) return 0;
Further :
c = MIN(count, MIN(SERIAL_XMIT_SIZE - info->xmit_cnt - 1, SERIAL_XMIT_SIZE - info->xmit_head)); if (c <= 0) break;
=> info->xmit_cnt and info->xmit_head are signed ints. If you encounter memory corruption (eg: during your ethernet transfers) and those get negative, nothing prevents the buffer from being overwritten past the end.
Further :
if (from_user) { down(&tmp_buf_sem); copy_from_user(tmp_buf, buf, c); c = MIN(c, MIN(SERIAL_XMIT_SIZE - info->xmit_cnt - 1, SERIAL_XMIT_SIZE - info->xmit_head)); ^^^^^^^^^^^^^^^^^^ memcpy(info->xmit_buf + info->xmit_head, tmp_buf, c); up(&tmp_buf_sem); } else
=> What the hell is this ? c was assigned the same value above, so we get : c = MIN(MIN(count, MIN(SERIAL_XMIT_SIZE - info->xmit_cnt - 1, SERIAL_XMIT_SIZE - info->xmit_head)), MIN(SERIAL_XMIT_SIZE - info->xmit_cnt - 1, SERIAL_XMIT_SIZE - info->xmit_head));
I'm not sure this was what the developper originally intented to do, but although useless, it does not seem incorrect. However, I don't know if he wanted to further reduce the buffer for any reason.
Also, it appears that nothing prevents any code running outside the loop from changing info->xmit_buf between the restore_flags() and the cli(). I don't know if this is functionnaly possible, but at least it is possible by memory corruption (eg: padding too large for a packet and writing zeroes past the end of one buffer).
You should definitely add printks or at least double checks everywhere within this loop I think.
That's all I can tell, I don't know this platform at all.
Regards, Willy
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