Messages in this thread | | | From | (Eric W. Biederman) | Date | Fri, 25 Apr 2014 14:43:42 -0700 | Subject | Re: Kernel panic at Ubuntu: IMA + Apparmor |
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Al Viro <viro@ZenIV.linux.org.uk> writes:
> On Fri, Apr 25, 2014 at 01:45:17PM -0700, Eric W. Biederman wrote: > >> IMA-appraisal is fundamentally broken because I can take a mandatory >> file lock and prevent IMA-apprasial. >> >> Using kernel_read is what allows this. >> >> > Isn't it a clear motivating case??? >> >> kernel_read is not appropriate for IMA use. The rest of this is just >> the messenger. >> >> IMA needs to use a cousin of kernel_read that operates at a lower level >> than vfs_read. A function that all of the permission checks and the >> fsnotify work. > > It's worse than that, actually ;-/ IMA hooks in __fput() have interesting > interplay with revoke-related stuff as well. Another very messy thing in > the same area is that it actually does ->read() from under ->i_mutex, leading > to all kinds of interesting locking issues... > > I doubt that your "let's open-code vfs_read() guts" would be a good idea; > if nothing else, it might make more sense to make rw_verify_area() skip > the mandlock and security theatre when called in such situation. > > What a mess... ;-/
Agreed.
All I really meant is that vfs_read does too much, so it probably needs to be refactored for this case. But fsnotify_read, add_rchar, and inc_syscr all seem inappropriate.
So I think we might be able to get away with something like this:
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; }
How much of the rest we do really would seem to depend on how valuable the sanity checks are.
This area of code keeps evolving enough that I don't see how we could possibly avoid going through helper functions to figure out which file ops we want to use this week.
Eric
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