Tuesday, December 29, 2009


More than five years ago Jakub Jelinek implemented object size checking in GCC. This feature (combined with GLIBC runtime checks) helps to detect many buffer overflows, both compile-time and run-time.  Of course, this brings some limitations to code.

Since then many distibutions (ALT Linux, Gentoo, OpenSUSE, Owl/*/Linux) turned this feature on by default. But there were those who resisted...

In February, 2007 patch from OpenSUSE was offered to Vim developers. Almost immediately it was rejected with resolution "The problem is in the compiler, so fix the compiler".

Now to the funny part.

Patch 7.2.044
Problem: Crash because of STRCPY() being over protective of the destination
size. (Dominique Pelle)
Solution: Add -D_FORTIFY_SOURCE=1 to CFLAGS. Use an intermediate variable
for the pointer to avoid a warning.

Patch 7.2.251 (after 7.2.044)
Problem: Compiler adds invalid memory bounds check.
Solution: Remove _FORTIFY_SOURCE=2 from CFLAGS. (Dominique Pelle)

Patch 7.2.316
Problem: May get multiple _FORTIFY_SOURCE arguments. (Tony Mechelynck)
Solution: First remove all these arguments and then add the one we want.
(Dominique Pelle)

I have a great citation for that case - this "won't solve the problem, only create the illusion that it works".

Heavy New Year, everyone, and double-check code that you intend to use in your usual life.

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