Affected: Linux

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

wifi: rtlwifi: Drastically reduce the attempts to read efuse in case of failures

Syzkaller reported a hung task with uevent_show() on stack trace. That specific issue was addressed by another commit [0], but even with that fix applied (for example, running v6.12-rc5) we face another type of hung task that comes from the same reproducer [1]. By investigating that, we could narrow it to the following path:

(a) Syzkaller emulates a Realtek USB WiFi adapter using raw-gadget and dummy_hcd infrastructure.

(b) During the probe of rtl8192cu, the driver ends-up performing an efuse read procedure (which is related to EEPROM load IIUC), and here lies the issue: the function read_efuse() calls read_efuse_byte() many times, as loop iterations depending on the efuse size (in our example, 512 in total).

This procedure for reading efuse bytes relies in a loop that performs an I/O read up to *10k* times in case of failures. We measured the time of the loop inside read_efuse_byte() alone, and in this reproducer (which involves the dummy_hcd emulation layer), it takes 15 seconds each. As a consequence, we have the driver stuck in its probe routine for big time, exposing a stack trace like below if we attempt to reboot the system, for example:

task:kworker/0:3 state:D stack:0 pid:662 tgid:662 ppid:2 flags:0x00004000 Workqueue: usb_hub_wq hub_event Call Trace: __schedule+0xe22/0xeb6 schedule_timeout+0xe7/0x132 __wait_fo…