CVE-2023-52587

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

IB/ipoib: Fix mcast list locking

Releasing the priv->lock while iterating the priv->multicast_list in ipoib_mcast_join_task() opens a window for ipoib_mcast_dev_flush() to remove the items while in the middle of iteration. If the mcast is removed while the lock was dropped, the for loop spins forever resulting in a hard lockup (as was reported on RHEL 4.18.0-372.75.1.el8_6 kernel):

Task A (kworker/u72:2 below)       | Task B (kworker/u72:0 below)
-----------------------------------+-----------------------------------
ipoib_mcast_join_task(work)        | ipoib_ib_dev_flush_light(work)
  spin_lock_irq(&priv->lock)       | __ipoib_ib_dev_flush(priv, ...)
  list_for_each_entry(mcast,       | ipoib_mcast_dev_flush(dev = priv->dev)
      &priv->multicast_list, list) |
    ipoib_mcast_join(dev, mcast)   |
      spin_unlock_irq(&priv->lock) |
                                   |   spin_lock_irqsave(&priv->lock, flags)
                                   |   list_for_each_entry_safe(mcast, tmcast,
                                   |                  &priv->multicast_list, list)
                                   |     list_del(&mcast->list);
                                   |     list_add_tail(&mcast->list, &remove_list)
                                   |   spin_unlock_irqrestore(&priv->lock, flags)
      spin_lock_irq(&priv->lock)   |
                                   |   ipoib_mcast_remove_list(&remove_list)

(Here, mcast is no longer on the | listforeachentrysafe(mcast, tmcast, priv->multicast_list and we keep | removelist, list) spinning on the remove_list of | >>> waitfor_completion(&mcast->done) the other thread which is blocked | and the list is still valid on | it's stack.)

Fix this by keeping the lock held and changing to GFP_ATOMIC to prevent eventual sleeps. Unfortunately we could not reproduce the lockup and confirm this fix but based on the code review I think this fix should address such lockups.

crash> bc 31

PID: 747 TASK: ff1c6a1a007e8000 CPU: 31 COMMAND: "kworker/u72:2"

[exception RIP: ipoib_mcast_join_task+0x1b1]
RIP: ffffffffc0944ac1  RSP: ff646f199a8c7e00  RFLAGS: 00000002
RAX: 0000000000000000  RBX: ff1c6a1a04dc82f8  RCX: 0000000000000000
                              work (&priv->mcast_task{,.work})
RDX: ff1c6a192d60ac68  RSI: 0000000000000286  RDI: ff1c6a1a04dc8000
       &mcast->list
RBP: ff646f199a8c7e90   R8: ff1c699980019420   R9: ff1c6a1920c9a000
R10: ff646f199a8c7e00  R11: ff1c6a191a7d9800  R12: ff1c6a192d60ac00
                                                     mcast
R13: ff1c6a1d82200000  R14: ff1c6a1a04dc8000  R15: ff1c6a1a04dc82d8
       dev                    priv (&priv->lock)     &priv->multicast_list (aka head)
ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0018

--- <NMI exception stack> --- #5 [ff646f199a8c7e00] ipoibmcastjointask+0x1b1 at ffffffffc0944ac1 [ibipoib] #6 [ff646f199a8c7e98] processonework+0x1a7 at ffffffff9bf10967

crash> rx ff646f199a8c7e68 ff646f199a8c7e68: ff1c6a1a04dc82f8 <<< work = &priv->mcast_task.work

crash> list -hO ipoibdevpriv.multicast_list ff1c6a1a04dc8000 (empty)

crash> ipoibdevpriv.mcasttask.work.func,mcastmutex.owner.counter ff1c6a1a04dc8000 mcasttask.work.func = 0xffffffffc0944910 <ipoib_mcast_join_task>, mcastmutex.owner.counter = 0xff1c69998efec000

crash> b 8

PID: 8 TASK: ff1c69998efec000 CPU: 33 COMMAND: "kworker/u72:0"

#3 [ff646f1980153d50] waitforcompletion+0x96 at ffffffff9c7d7646 #4 [ff646f1980153d90] ipoibmcastremovelist+0x56 at ffffffffc0944dc6 [ibipoib] #5 [ff646f1980153de8] ipoibmcastdevflush+0x1a7 at ffffffffc09455a7 [ibipoib] #6 [ff646f1980153e58] _ipoibibdevflush+0x1a4 at ffffffffc09431a4 [ib_ipoib] #7 [ff ---truncated---