CVE-2025-68245

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

net: netpoll: fix incorrect refcount handling causing incorrect cleanup

commit efa95b01da18 (netpoll: fix use after free) incorrectly ignored the refcount and prematurely set dev->npinfo to NULL during netpoll cleanup, leading to improper behavior and memory leaks.

Scenario causing lack of proper cleanup:

1. A netpoll is associated with a NIC (e.g., eth0) and netdev->npinfo is allocated, and refcnt = 1

   • Keep in mind that npinfo is shared among all netpoll instances. In this case, there is just one.

2. Another netpoll is also associated with the same NIC and npinfo->refcnt += 1.

   • Now dev->npinfo->refcnt = 2;
   • There is just one npinfo associated to the netdev.

3. When the first netpolls goes to clean up:

   • The first cleanup succeeds and clears np->dev->npinfo, ignoring refcnt.
     • It basically calls RCU_INIT_POINTER(np->dev->npinfo, NULL);
   • Set dev->npinfo = NULL, without proper cleanup
   • No ->ndo_netpoll_cleanup() is either called

4. Now the second target tries to clean up

   • The second cleanup fails because np->dev->npinfo is already NULL.
     • In this case, ops->ndo_netpoll_cleanup() was never called, and the skb pool is not cleaned as well (for the second netpoll instance)

• This leaks npinfo and skbpool skbs, which is clearly reported by kmemleak.

Revert commit efa95b01da18 (netpoll: fix use after free) and adds clarifying comments emphasizing that npinfo cleanup should only happen once the refcount reaches zero, ensuring stable and correct netpoll behavior.

Affected Software

References

• https://git.kernel.org/stable/c/49c8d2c1f94cc2f4d1a108530d7ba52614b874c2
• https://git.kernel.org/stable/c/4afd4ebbad52aa146838ec23082ba393e426a2bb
• https://git.kernel.org/stable/c/890472d6fbf062e6de7fdd56642cb305ab79d669
• https://git.kernel.org/stable/c/8e6a50edad11e3e1426e4c29e7aa6201f3468ac2
• https://git.kernel.org/stable/c/9a51b5ccd1c79afec1c03a4e1e6688da52597556
• https://git.kernel.org/stable/c/9b0bb18b4b9dc017c1825a2c5e763615e34a1593
• https://git.kernel.org/stable/c/c645693180a98606c430825223d2029315d85e9d
• https://git.kernel.org/stable/c/c79a6d9da29219616b118a3adce9a14cd30f9bd0