On Sat, Apr 13, 2019 at 10:27:00AM -0700, Linus Torvalds wrote: > And I'd really like to have people (Al?) look at this and go "yeah, > makes sense". I do think that moving to a model where we wither have a > (properly locked) file position or no pos pointer at all is the right > model (ie I'd really like to get rid of the mixed case), but there > might be some practical problem that makes it impractical. > > Because the *real* problem with the mixed case is not "insane people > who do bad things might get odd results". No, the real problem with > the mixed case is that it could be a security issue (ie: one process > intentionally changes the file position just as another process is > going a 'read' and then avoids some limit test because the limit test > was done using the old 'pos' value but the actual IO was done using > the new one). > > So I suspect that we will have to either > > - get rid of the mixed case entirely (and do only properly locked > f_pos accesses or pass is a NULL f_pos) Good luck. Character devices get no exclusion often do use position are many might be buried behind several layers of indirection ... and often left unmaintained for a decade or two IOW, I don't see how you'd go about eliminating the mixed case...
