On Fri, Jan 06, 2023 at 05:12:57PM -0500, Hang Zhang wrote: > On Fri, Jan 6, 2023 at 4:19 PM Daniel Vetter <daniel@xxxxxxxx> wrote: > > On Fri, Jan 06, 2023 at 03:25:14PM -0500, Hang Zhang wrote: > > > On Fri, Jan 6, 2023 at 3:05 PM Daniel Vetter <daniel@xxxxxxxx> wrote: > > > > On Fri, Jan 06, 2023 at 02:58:27PM -0500, Hang Zhang wrote: > > > > > On Fri, Jan 6, 2023 at 1:59 PM Daniel Vetter <daniel@xxxxxxxx> wrote: > > > > > BTW, if this is worthed a fix and the performance of console_lock() is a > > > > > major concern, then I think there may be alternative solutions like adding > > > > > a lock_fb_info() to the free call chain - if that's better in performance, > > > > > or maybe selectively protect the matroxfb ioctl but not vblank ioctl as you > > > > > mentioned. > > > > > > > > Please start out with explaining what kind of bug your checker is seeing, > > > > and why. Not how you're trying to fix it. Because I'm pretty sure there > > > > isn't a bug, but since I've already spent a pile of time looking at this, > > > > I want to make sure. > > > > > > We are sorry for the inconvenience caused, we'll follow these practices and > > > guidelines in the future. Thank you! > > > > Once more: Please explain what you're static checker is seeing. I want to > > understanding this, and I'm hoping at least someone involved in this > > static checker can explain what it thinks is going on. > > > > Thanks, Daniel > > -- > > Daniel Vetter > > Software Engineer, Intel Corporation > > http://blog.ffwll.ch > > Thank you for your interest, Daniel. The checker tries first to find > the free and > use sites of a certain object (in this case "fb_info"), then reason > about whether > the use can actually happen after the free (e.g., taking into account > factors like > state set/check, locks, etc.), if so, it will flag a potential > use-after-free. As a static > checker, is doesn't execute a program or generate a PoC. We then manually > review each flagged issue by inspecting all related code. In this > case, the checker > (and us) are unaware of the lifetime management logic, which may cause > problems. Lifetime management is and absolute basic part in the linux kernel. So if your checker flags every free which isn't protected by a lock, then you'll creating endless amounts of false positives. Is this really what you're doing? I'm still very confused ... -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
