EDIT2: Thanks to the efforts of Jake Edge who noticed our presentation, /proc/pid/stat information leak is now at least partially patched in mainline kernel, since 220.127.116.11
EDIT1: This is featured in an LWN article by Jake Edge
Tavis Ormandy and myself talked about locally bypassing address space layout randomization (ASLR) in Linux in a lightning talk at CanSecWest.
From Linux 2.6.12 to Linux 2.6.21, you could completely bypass ASLR when targeting local processes by reading /proc/pid/maps. Since Linux 2.6.22, if you cannot ptrace "pid", then you will see an empty /proc/pid/maps.
It has been known for at least 7 years now that /proc/pid/stat and /proc/pid/wchan could also leak sensitive information. Reading this information has been prevented in GRSecurity since the beginning as well as in this patch.
The question was: could you exploit this information to bypass ASLR in practice?
If you want to find out, it's easy: we've just published the slides and Tavis' tool!