x86/apic/vector: Prevent hlist corruption and leaks

Several people observed the WARN_ON() in irq_matrix_free() which triggers when the caller tries to free an vector which is not in the allocation range. Song provided the trace information which allowed to decode the root cause.

The rework of the vector allocation mechanism failed to preserve a sanity check, which prevents setting a new target vector/CPU when the previous affinity change has not fully completed.

As a result a half finished affinity change can be overwritten, which can cause the leak of a irq descriptor pointer on the previous target CPU and double enqueue of the hlist head into the cleanup lists of two or more CPUs. After one CPU cleaned up its vector the next CPU will invoke the cleanup handler with vector 0, which triggers the out of range warning in the matrix allocator.

Prevent this by checking the apic_data of the interrupt whether the move_in_progress flag is false and the hlist node is not hashed. Return -EBUSY if not.

This prevents the damage and restores the behaviour before the vector allocation rework, but due to other changes in that area it also widens the chance that user space can observe -EBUSY. In theory this should be fine, but actually not all user space tools handle -EBUSY correctly. Addressing that is not part of this fix, but will be addressed in follow up patches.

Fixes 69cde0004a4b ("x86/vector: Use matrix allocator for vector assignment")

Reported-by Dmitry Safonov <[email protected]>

Reported-by Tariq Toukan <[email protected]>

Reported-by Song Liu <[email protected]>

Signed-off-by Thomas Gleixner <[email protected]>

Cc [email protected]

---
 arch/x86/kernel/apic/vector.c |    9 +++++++++
 1 file changed, 9 insertions(+)

arch/x86/kernel/apic/vector.c +9 -0

@@ -235,6 +235,15 @@ static int allocate_vector(struct irq_da
        if (vector && cpu_online(cpu) && cpumask_test_cpu(cpu, dest))
                return 0;
 
+       /*
+        * Careful here. @apicd might either have move_in_progress set or
+        * be enqueued for cleanup. Assigning a new vector would either
+        * leave a stale vector on some CPU around or in case of a pending
+        * cleanup corrupt the hlist.
+        */
+       if (apicd->move_in_progress || !hlist_unhashed(&apicd->clist))
+               return -EBUSY;
+
        vector = irq_matrix_alloc(vector_matrix, dest, resvd, &cpu);
        if (vector > 0)
                apic_update_vector(irqd, vector, cpu);