AZL-86888

In the Linux kernel, the following vulnerability has been resolved:

ptrace: slightly saner 'get_dumpable()' logic

The 'dumpability' of a task is fundamentally about the memory image of the task - the concept comes from whether it can core dump or not - and makes no sense when you don't have an associated mm.

And almost all users do in fact use it only for the case where the task has a mm pointer.

But we have one odd special case: ptracemayaccess() uses 'dumpable' to check various other things entirely independently of the MM (typically explicitly using flags like PTRACEMODEREAD_FSCREDS). Including for threads that no longer have a VM (and maybe never did, like most kernel threads).

It's not what this flag was designed for, but it is what it is.

The ptrace code does check that the uid/gid matches, so you do have to be uid-0 to see kernel thread details, but this means that the traditional "drop capabilities" model doesn't make any difference for this all.

Make it all make a bit more sense by saying that if you don't have a MM pointer, we'll use a cached "last dumpability" flag if the thread ever had a MM (it will be zero for kernel threads since it is never set), and require a proper CAPSYSPTRACE capability to override.