Messages in this thread | | | Subject | Re: Kernel panic at Ubuntu: IMA + Apparmor | From | Mimi Zohar <> | Date | Tue, 29 Apr 2014 09:00:12 -0400 |
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My apologies for those receiving this post a 2nd time. The original post never made it the mailing lists ...
On Fri, 2014-04-25 at 15:25 -0700, Eric W. Biederman wrote: > Al Viro <viro@ZenIV.linux.org.uk> writes: > > > On Fri, Apr 25, 2014 at 02:43:42PM -0700, Eric W. Biederman wrote: > > > >> ssize_t __vfs_read(struct file *file, char __user *buf, size_t count, loff_t *pos) > >> { > >> ssize_t ret; > >> > >> if (!(file->f_mode & FMODE_READ)) > >> return -EBADF; > >> if (!file->f_op->read && !file->f_op->aio_read) > >> return -EINVAL; > >> if (unlikely(!access_ok(VERIFY_WRITE, buf, count))) > >> return -EFAULT; > >> > >> if (ret >= 0) { > >> count = ret; > >> if (file->f_op->read) > >> ret = file->f_op->read(file, buf, count, pos); > >> else > >> ret = do_sync_read(file, buf, count, pos); > >> } > >> > >> return ret; > >> } > > > > ... which lacks the f_pos wraparound, etc. checks done by rw_verify_area(). > > IOW, it's one more place to grep through while verifying that ->read() > > et.al. do not get called with such arguments. > > Agreed it must be done more delicately than my sketch. I am not > familiar with how much value such sanity checks add. Especially when > the read is not coming from a potentially hostile userspace.
Sorry for the delay in commenting, imap problems. This sounds like a plausible solution, similar to __vfs_setxattr_noperm() vs. __vfs_setxattr().
> > fanotify probably could be skipped - ask the security circus crowd about > > that one, it's their bast^Wbaby. > > When the point is having a factor of read that skips the security circus > I think it makes sense to skip this too. At least as a starting > position.
Right, fsnotify*() is meant for userspace access, not kernel access. CC'ing Eric Paris for comment.
> > add_rchar() and inc_syscr()... depends on > > whether you want those reads hidden from accounting. > > I doubt it matters in practice, the code is cheap. > > Still it feels wrong to account reads to a task that did not ask for > them. It feels more correct to account that kind of read into a > different bucket. Say the reads performed by the kernel for mysterious > kernel activities.
Ok. So who are the interested parties that need to be included in this discussion?
thanks,
Mimi
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