CVE-2023-53087

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

drm/i915/active: Fix misuse of non-idle barriers as fence trackers

Users reported oopses on list corruptions when using i915 perf with a

number of concurrently running graphics applications. Root cause analysis

pointed at an issue in barrier processing code -- a race among perf open /

close replacing active barriers with perf requests on kernel context and

concurrent barrier preallocate / acquire operations performed during user

context first pin / last unpin.

When adding a request to a composite tracker, we try to reuse an existing

fence tracker, already allocated and registered with that composite. The

tracker we obtain may already track another fence, may be an idle barrier,

or an active barrier.

If the tracker we get occurs a non-idle barrier then we try to delete that

barrier from a list of barrier tasks it belongs to. However, while doing

that we don't respect return value from a function that performs the

barrier deletion. Should the deletion ever fail, we would end up reusing

the tracker still registered as a barrier task. Since the same structure

field is reused with both fence callback lists and barrier tasks list,

list corruptions would likely occur.

Barriers are now deleted from a barrier tasks list by temporarily removing

the list content, traversing that content with skip over the node to be

deleted, then populating the list back with the modified content. Should

that intentionally racy concurrent deletion attempts be not serialized,

one or more of those may fail because of the list being temporary empty.

Related code that ignores the results of barrier deletion was initially

introduced in v5.4 by commit d8af05ff38ae ("drm/i915: Allow sharing the

idle-barrier from other kernel requests"). However, all users of the

barrier deletion routine were apparently serialized at that time, then the

issue didn't exhibit itself. Results of git bisect with help of a newly

developed igt@gem_barrier_race@remote-request IGT test indicate that list

corruptions might start to appear after commit 311770173fac ("drm/i915/gt:

Schedule request retirement when timeline idles"), introduced in v5.5.

Respect results of barrier deletion attempts -- mark the barrier as idle

only if successfully deleted from the list. Then, before proceeding with

setting our fence as the one currently tracked, make sure that the tracker

we've got is not a non-idle barrier. If that check fails then don't use

that tracker but go back and try to acquire a new, usable one.

v3: use unlikely() to document what outcome we expect (Andi),

- fix bad grammar in commit description.

v2: no code changes,

- blame commit 311770173fac ("drm/i915/gt: Schedule request retirement

when timeline idles"), v5.5, not commit d8af05ff38ae ("drm/i915: Allow

sharing the idle-barrier from other kernel requests"), v5.4,

- reword commit description.

(cherry picked from commit 506006055769b10d1b2b4e22f636f3b45e0e9fc7)