igb: remove napi_synchronize() in igb_down()

Overview

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

igb: remove napi_synchronize() in igb_down()

When an AF_XDP zero-copy application terminates abruptly (e.g., kill -9), the XSK buffer pool is destroyed but NAPI polling continues. igb_clean_rx_irq_zc() repeatedly returns the full budget, preventing napi_complete_done() from clearing NAPI_STATE_SCHED.

igb_down() calls napi_synchronize() before napi_disable() for each queue vector. napi_synchronize() spins waiting for NAPI_STATE_SCHED to clear, which never happens. igb_down() blocks indefinitely, the TX watchdog fires, and the TX queue remains permanently stalled.

napi_disable() already handles this correctly: it sets NAPI_STATE_DISABLE. After a full-budget poll, __napi_poll() checks napi_disable_pending(). If set, it forces completion and clears NAPI_STATE_SCHED, breaking the loop that napi_synchronize() cannot.

napi_synchronize() was added in commit 41f149a285da ("igb: Fix possible panic caused by Rx traffic arrival while interface is down"). napi_disable() provides stronger guarantees: it prevents further scheduling and waits for any active poll to exit. Other Intel drivers (ixgbe, ice, i40e) use napi_disable() without a preceding napi_synchronize() in their down paths.

Remove redundant napi_synchronize() call and reorder napi_disable() before igb_set_queue_napi() so the queue-to-NAPI mapping is only cleared after polling has fully stopped.

Affected

• Linux >= 2c6196013f84651772388a86dfd4bb033d0c0d45 < 4700471775746058c962ded6e659bf908fd76e13
• Linux >= 2c6196013f84651772388a86dfd4bb033d0c0d45 < 27f5997686ee7fb7ac01be72b2010f168a3409fc
• Linux >= 2c6196013f84651772388a86dfd4bb033d0c0d45 < b1e067240379f950a0022208e0685f3465c211cb
• Linux 6.14

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.