[Bug 305901] Re: Intrepid gcc -O2 breaks string appending with sprintf(), due to fortify source patch

[Anders Kaseorg]

** Also affects: 4g8 (Ubuntu)
   Importance: Undecided
       Status: New

** Description changed:

  Binary package hint: gcc-4.3
  
  In Hardy and previous releases, one could use statements such as
    sprintf(buf, "%s %s%d", buf, foo, bar);
  to append formatted text to a buffer buf.  Intrepid’s gcc-4.3, which has fortify source turned on by default when compiling with -O2, breaks this pattern.  This introduced mysterious bugs into an application I was compiling (the BarnOwl IM client).
  
  Test case: gcc -O2 sprintf-test.c -o sprintf-test
  <http://web.mit.edu/andersk/Public/sprintf-test.c>:
    #include <stdio.h>
    char buf[80] = "not ";
    int main()
    {
        sprintf(buf, "%sfail", buf);
        puts(buf);
        return 0;
    }
  This outputs "not fail" in Hardy, and "fail" in Intrepid.
  
  The assembly output shows that the bug has been introduced by replacing
  the sprintf(buf, "%sfail", buf) call with __sprintf_chk(buf, 1, 80,
  "%sfail", buf).  A workaround is to disable fortify source (gcc
  -U_FORTIFY_SOURCE).
  
  One might argue that this usage of sprintf() is questionable.  I had
  been under the impression that it is valid, and found many web pages
  that agree with me, though I was not able to find an authoritative
  statement either way citing the C specification.  I decided to
  investigate how common this pattern is in real source code.
  
  You can search a source file for instances of it with this regex:
-   perl -ne 'print if m/sprintf\s*\(\s*([^,]*)\s*,\s*"%s[^"]*"\s*,\s*\1\s*,/'
+   pcregrep -M 'sprintf\s*\(\s*([^,]*)\s*,\s*"%s[^"]*"\s*,\s*\1\s*,'
  
  To determine how common the pattern is, I wrote a script to track down instances using Google Code Search, and found 2888 matches:
    <http://web.mit.edu/andersk/Public/sprintf-results>
  (For the curious: the script uses a variant of the regex above.  I had to use a binary search to emulate backreferences, which aren’t supported by Code Search, so the script makes 46188 queries and takes a rather long time to run.  The source is available at <http://web.mit.edu/andersk/Public/sprintf-codesearch.py>.)
  
  My conclusion is that, whether or not this pattern is technically
  allowed by the C specification, it is common enough that the compiler
  should be fixed, if that is at all possible.

** Also affects: abiword (Ubuntu)
   Importance: Undecided
       Status: New

-- 
Intrepid gcc -O2 breaks string appending with sprintf(), due to fortify source patch
https://bugs.launchpad.net/bugs/305901
You received this bug notification because you are a member of Ubuntu
Server Team, which is subscribed to nagios-plugins in ubuntu.