> From: Mimi Zohar [mailto:zohar@xxxxxxxxxxxxx] > Sent: Monday, February 14, 2022 11:33 PM > On Mon, 2022-02-14 at 17:05 +0000, Roberto Sassu wrote: > > > From: Mimi Zohar [mailto:zohar@xxxxxxxxxxxxx] > > > Sent: Sunday, February 13, 2022 2:06 PM > > > Hi Roberto, > > > > > > On Fri, 2022-02-11 at 11:48 +0100, Roberto Sassu wrote: > > > > __ima_inode_hash() checks if a digest has been already calculated by > > > > looking for the integrity_iint_cache structure associated to the passed > > > > inode. > > > > > > > > Users of ima_file_hash() and ima_inode_hash() (e.g. eBPF) might be > > > > interested in obtaining the information without having to setup an IMA > > > > policy so that the digest is always available at the time they call one of > > > > those functions. > > > > > > > > Open a new file descriptor in __ima_inode_hash(), so that this function > > > > could invoke ima_collect_measurement() to calculate the digest if it is not > > > > available. Still return -EOPNOTSUPP if the calculation failed. > > > > > > > > Instead of opening a new file descriptor, the one from ima_file_hash() > > > > could have been used. However, since ima_inode_hash() was created to > > > obtain > > > > the digest when the file descriptor is not available, it could benefit from > > > > this change too. Also, the opened file descriptor might be not suitable for > > > > use (file descriptor opened not for reading). > > > > > > > > This change does not cause memory usage increase, due to using a > temporary > > > > integrity_iint_cache structure for the digest calculation, and due to > > > > freeing the ima_digest_data structure inside integrity_iint_cache before > > > > exiting from __ima_inode_hash(). > > > > > > > > Finally, update the test by removing ima_setup.sh (it is not necessary > > > > anymore to set an IMA policy) and by directly executing /bin/true. > > > > > > > > Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx> > > > > > > Although this patch doesn't directly modify either ima_file_hash() or > > > ima_inode_hash(), this change affects both functions. ima_file_hash() > > > was introduced to be used with eBPF. Based on Florent's post, changing > > > the ima_file_hash() behavor seems fine. Since I have no idea whether > > > anyone is still using ima_inode_hash(), perhaps it would be safer to > > > limit this behavior change to just ima_file_hash(). > > > > Hi Mimi > > > > ok. > > > > I found that just checking that iint->ima_hash is not NULL is not enough > > (ima_inode_hash() might still return the old digest after a file write). > > Should I replace that check with !(iint->flags & IMA_COLLECTED)? > > Or should I do only for ima_file_hash() and recalculate the digest > > if necessary? > > Updating the file hash after each write would really impact IMA > performance. If you really want to detect any file change, no matter > how frequently it occurs, your best bet would be to track i_generation > and i_version. Stefan is already adding "i_generation" for IMA > namespacing. I just wanted the ability to get a fresh digest after a file opened for writing is closed. Since in my use case I would not use an IMA policy, that would not be a problem. Thanks Roberto HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063 Managing Director: Li Peng, Zhong Ronghua > > > Please update the ima_file_hash() doc. While touching this area, I'd > > > appreciate your fixing the first doc line in both ima_file_hash() and > > > ima_inode_hash() cases, which wraps spanning two lines. > > > > Did you mean to make the description shorter or to have everything > > in one line? According to the kernel documentation (kernel-doc.rst), > > having the brief description in multiple lines should be fine. > > Thanks for checking kernel-doc. The "brief description" not wrapping > across multiple lines did in fact change. > > > > Please split the IMA from the eBPF changes. > > > > Ok. > > -- > thanks, > > Mimi
