> Thanks for your reply. > > > You are providing a program with an additional gid. The program has > > not been coded be aware of that gid. Two potentially different > > filesystem views now exist within the program, depending on the g=rwx > > bits of directories and files in the tree. The program is no longer > > operating in a world-view it was designed for. > > Could you be more precise on this point? I mean: if I correctly > understand, you said that this can induce unwanted behavior due to the > fact that, for example, firefox suppose it has the uid and gid of the > user who launch it (and not a different egid)? > > If I'am right, does this can really mater if the egid is the one of a > group that only own one (executable) file in the whole system whith only > read and execute permission on it?
Make a copy of ls, and add the setgid bit to it. Play around with it for a while, including using chmod on various files and directories. It shouldn't take you long to realize that setuid/setgid should only be set on programs that are specifically written for that.
