Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=831

IOSurfaceRootUserClient stores a task struct pointer (passed in via IOServiceOpen) in the field at +0xf0 without taking a reference.

By killing the corrisponding task we can free this pointer leaving the user client with a dangling pointer. We can get this pointer used
by calling the create_surface_fast_path external method which will try to read and use the memory map off of the free'd task struct.

This bug could be leveraged for kernel memory corruption and is reachable from interesting sandboxes including safari and chrome.

build: clang -o surfaceroot_uaf surfaceroot_uaf.c -framework IOKit

You should set gzalloc_min=1024 gzalloc_max=2048 or similar to actually fault on the UaF - otherwise you might see some weird panics!

tested on OS X 10.11.5 (15F34) on MacBookAir5,2

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another PoC for "task_t considered harmful"
since 10.11.6 blocks us from creating userclients with other task's task ports
this time we create an IOSurface in the child and send back a send right to that
IOSurface to the parent (rather than sending the child's task port.)

The child then execs a suid-root binary which blocks on stderr and the parent
creates an IOSurface which maps any (writable?) page of the euid-0 process into theirs.
Overwrite a function pointer and win.

No race conditions because the task struct pointer is on the kernel heap, not the stack.


Proofs of Concept:
https://github.com/offensive-security/exploitdb-bin-sploits/raw/master/bin-sploits/40653.zip