On 3/12/2024 11:51 AM, Casey Schaufler wrote:
On 3/12/2024 11:14 AM, Fan Wu wrote:
On 3/11/2024 8:07 PM, Eric Biggers wrote:
On Mon, Mar 11, 2024 at 07:57:12PM -0700, Eric Biggers wrote:
As I've said before, this commit message needs some work. It
currently doesn't
say anything about what the patch actually does.
BTW, please make sure you're Cc'ing the fsverity mailing list
(fsverity@xxxxxxxxxxxxxxx), not fscrypt
(linux-fscrypt@xxxxxxxxxxxxxxx).
Also, I thought this patch was using a new LSM hook, but I now see
that you're
actually abusing the existing security_inode_setsecurity() LSM hook.
Currently
that hook is called when an xattr is set. I don't see any precedent for
overloading it for other purposes. This seems problematic, as it
means that a
request to set an xattr with the name you chose
("fsverity.builtin-sig") will be
interpreted by LSMs as the fsverity builtin signature. A dedicated
LSM hook may
be necessary to avoid issues with overloading the existing xattr hook
like this.
- Eric
Thanks for the suggestion. I found that using
security_inode_setsecurity() causes issues with SMACK's
inode_setsecurity() hook. I will crate a dedicated new hook like
security_inode_setsig() in the next version.
What is the issue you encountered with the Smack hook?
The current hook call for saving file signature will fail at
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/security/smack/smack_lsm.c#n2855
.
The issue is file signature size is larger than SMK_LONGLABEL so if
SMACK is enabled the SMACK's hook will return -EINVAL, which prevents us
to use security_inode_setsecurity() to save file signature into security
blob.
We could also make security_inode_setsecurity() more generic instead of
for xattr only, any suggestions?
-Fan
