[Bug 185242] New: ioctl default minimum argument length of 256 should be restored

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Sun Mar 12 18:59:07 UTC 2006

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           Summary: ioctl default minimum argument length of 256 should be
           Product: Fedora Core
           Version: fc4
          Platform: All
               URL: http://rt.perl.org/rt3/Ticket/Display.html?id=38223
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: normal
         Component: perl
        AssignedTo: jvdias at redhat.com
        ReportedBy: jvdias at redhat.com
         QAContact: dkl at redhat.com
                CC: fedora-perl-devel-list at redhat.com,prockai at redhat.com

+++ This bug was initially created as a clone of Bug #185240 +++

Description of problem:
This is perl bug request ticket 38223 .

Owing to the fix for bug 171111, where the length bitfield of the ioctl 
number argument, which specifies the length of the optional RD ioctl output
third argument, was not being extracted correctly, and perl used 256 as the 
minimum length of the third argument in all cases, perl now does not ascribe 
any minimum length to the third argument unless the length bitfield is

This has the result that unless the length bitfield of the ioctl number is
specified, a third argument of a buffer with insufficient length for the
ioctl output will be overflowed, and perl will suffer a buffer overflow
and a potential memory access violation or memory corruption, 
as generated by the following code (from perlbug RT# 38223):

require 'sys/ioctl.ph';
die "no TIOCGWINSZ " unless defined &TIOCGWINSZ;
open(TTY, "+</dev/tty") or die "No tty: $!";
unless (ioctl(TTY, &TIOCGWINSZ, $winsize='')) {
die sprintf "$0: ioctl TIOCGWINSZ (%08x: $!)\n", &TIOCGWINSZ;
($row, $col, $xpixel, $ypixel) = unpack('S4', $winsize);
print "(row,col) = ($row,$col)";
print " (xpixel,ypixel) = ($xpixel,$ypixel)" if $xpixel || $ypixel;
print "\n";

Perl now correctly detects the buffer overflow:

Possible memory corruption: ioctl overflowed 3rd argument at ./bug38223.pl 
line 5.

This would not have occurred with perl versions before perl-5.8.6-18,
because the length of all the ioctl third output arguments was made a 
minimum of 256 bytes.

The overflow would not have occurred if the ioctl call had been :
  ioctl(TTY, &TIOCGWINSZ, $winsize='x'x16)
  ioctl(TTY, &TIOCGWINSZ | (16 << &_IOC_SIZESHIFT), $winsize='')

The default size of 256 has been restored in the latest upstream patch for 
this issue:

==== //depot/perl/perl.h#657 (text) ====
Index: perl/perl.h
--- perl/perl.h.~1~ Fri Jan 13 04:10:49 2006
+++ perl/perl.h Fri Jan 13 04:10:49 2006
@@ -2977,8 +2977,8 @@
# define IOCPARM_LEN(x) (((x) >> 16) & \ # IOCPARM_MASK)
# else
# if defined(_IOC_SIZE) && defined(__GLIBC__)
- /* on Linux systems we're safe */
-# define IOCPARM_LEN(x) _IOC_SIZE(x)
+ /* on Linux systems we're safe; except when we're not [perl #38223] */
+# define IOCPARM_LEN(x) (_IOC_SIZE(x) < 256 ? 256 : \ _IOC_SIZE(x))
# else
/* otherwise guess at what's safe */
# define IOCPARM_LEN(x) 256
End of Patch.

Version-Release number of selected component (if applicable):

How reproducible:

Steps to Reproduce:
Invoke a READ ioctl with a 0 length bitfield and and output buffer 
third argument of insufficient length to hold the potential ioctl output. 
Actual results:
Perl exits with error:
Possible memory corruption: ioctl overflowed 3rd argument

Expected results:
Perl should enforce a minimum length of 256 bytes for the ioctl output buffer.

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