[apparmor] Questions about AppArmor's Kernel Code

[Casey Schaufler]

On 7/26/2019 5:56 AM, Abhishek Vijeev wrote:
>
> Hi,
>
>
> I have a few questions about AppArmor's kernel code and would be grateful if you could kindly answer them.?
>
>
> 1) Why does AppArmor maintain two separate security blobs in cred->security as well as task-security for processes? For a simple project that requires associating a security context with every task, would it suffice to use just one of these?
>
>
> 2) There has been a change in the way security blobs are accessed from kernel version 4.18 to 5.2. I see that in v5.2, the?security blob's address is obtained by adding the size of the blob to the start address. Why has this change been made? (For reference:?https://github.com/torvalds/linux/blob/master/security/apparmor/include/cred.h#L24)
>
The change was made to allow multiple security modules to share the
blobs. The security module initialization replaces the size of the blobs
in apparmor_bob_sizes with their offsets in the blob. The addition you
see adds the offset, not the size.

>
> 3) I tried adding a custom field (pointer to a custom structure) to struct aa_profile, at exactly this point -?https://github.com/torvalds/linux/blob/master/security/apparmor/include/policy.h#L144. I have taken care to allocate and free memory for the pointer at the appropriate places (allocation is performed here -?https://github.com/torvalds/linux/blob/master/security/apparmor/policy_unpack.c#L671?and freeing is performed?here -?https://github.com/torvalds/linux/blob/master/security/apparmor/policy.c#L205).?However, while booting the kernel, it crashes?at the function 'security_prepare_creds( )', which I presume invokes 'apparmor_cred_prepare( )'. If I was, to assume for a moment that there are no bugs with my memory allocation code, is there any other reason why such a crash might have occurred??I have attached the kernel crash log?file?with this email for your kind?reference.?
>
>
> Thank you,
>
> Abhishek.
>
>
>
>