[apparmor] Questions about AppArmor's Kernel Code

[Abhishek Vijeev]

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)


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.


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