Talking about f_modown() and security_file_set_fowner(), it looks like there are some issues: On Fri, Aug 09, 2024 at 02:44:06PM +0200, Jann Horn wrote: > On Fri, Aug 9, 2024 at 12:59 PM Mickaël Salaün <mic@xxxxxxxxxxx> wrote: [...] > > BTW, I don't understand why neither SELinux nor Smack use (explicit) > > atomic operations nor lock. > > Yeah, I think they're sloppy and kinda wrong - but it sorta works in > practice mostly because they don't have to do any refcounting around > this? > > > And it looks weird that > > security_file_set_fowner() isn't called by f_modown() with the same > > locking to avoid races. > > True. I imagine maybe the thought behind this design could have been > that LSMs should have their own locking, and that calling an LSM hook > with IRQs off is a little weird? But the way the LSMs actually use the > hook now, it might make sense to call the LSM with the lock held and > IRQs off... > Would it be OK (for VFS, SELinux, and Smack maintainers) to move the security_file_set_fowner() call into f_modown(), especially where UID/EUID are populated. That would only call security_file_set_fowner() when the fown is actually set, which I think could also fix a bug for SELinux and Smack. Could we replace the uid and euid fields with a pointer to the current credentials? This would enables LSMs to not copy the same kind of credential informations and save some memory, simplify credential management, and improve consistency.
