Public bug reported: 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*,/' 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. ** Affects: gcc-4.3 (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 Bugs, which is subscribed to Ubuntu. -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
