On 10/1/2021 12:50 PM, Jann Horn wrote:
On Fri, Oct 1, 2021 at 9:36 PM Jann Horn jannh@google.com wrote:
On Fri, Oct 1, 2021 at 8:46 PM Casey Schaufler casey@schaufler-ca.com wrote:
On 10/1/2021 10:55 AM, Todd Kjos wrote:
Save the struct cred associated with a binder process at initial open to avoid potential race conditions when converting to a security ID.
Since binder was integrated with selinux, it has passed 'struct task_struct' associated with the binder_proc to represent the source and target of transactions. The conversion of task to SID was then done in the hook implementations. It turns out that there are race conditions which can result in an incorrect security context being used.
In the LSM stacking patch set I've been posting for a while (on version 29 now) I use information from the task structure to ensure that the security information passed via the binder interface is agreeable to both sides. Passing the cred will make it impossible to do this check. The task information required is not appropriate to have in the cred.
Why not? Why can't you put the security identity of the task into the creds?
Ah, I get it now, you're concerned about different processes wanting to see security contexts formatted differently (e.g. printing the SELinux label vs printing the AppArmor label), right?
That is correct.
But still, I don't think you can pull that information from the receiving task. Maybe the easiest solution would be to also store that in the creds? Or you'd have to manually grab that information when /dev/binder is opened.
I'm storing the information in the task security blob because that's the appropriate scope. Today the LSM hook is given both task_struct's. It's easy to compare to make sure the tasks are compatible. Adding the information to the cred would be yet another case where the scope of security information is wrong.