In the Linux kernel, the following vulnerability has been resolved: af_unix: Set gc_in_progress to true in unix_gc(). Igor Ushakov reporte

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

af_unix: Set gc_in_progress to true in unix_gc().

Igor Ushakov reported that unix_gc() could run with gc_in_progress
being false if the work is scheduled while running:

Thread 1 Thread 2 Thread 3

 1               unix_schedule_gc()           unix_schedule_gc()
 2               `- if (!gc_in_progress)      `- if (!gc_in_progress)
 3                  |- gc_in_progress = true     |
 4                  `- queue_work()              |

unix_gc() <----------------/ |
| |- gc_in_progress = true
... - queue_work() | | - gc_in_progress = false |
|
unix_gc() <---------------------------------------------'
|
... /* gc_in_progress == false */
|
`- gc_in_progress = false

unix_peek_fpl() relies on gc_in_progress not to confuse GC
by MSG_PEEK.

Let's set gc_in_progress to true in unix_gc().