net: ena: fix shift-out-of-bounds in exponential backoff

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

net: ena: fix shift-out-of-bounds in exponential backoff

The ENA adapters on our instances occasionally reset. Once recently

logged a UBSAN failure to console in the process:

UBSAN: shift-out-of-bounds in build/linux/drivers/net/ethernet/amazon/ena/ena_com.c:540:13

shift exponent 32 is too large for 32-bit type 'unsigned int'

CPU: 28 PID: 70012 Comm: kworker/u72:2 Kdump: loaded not tainted 5.15.117

Hardware name: Amazon EC2 c5d.9xlarge/, BIOS 1.0 10/16/2017

Workqueue: ena ena_fw_reset_device [ena]

Call Trace:

<TASK>

dump_stack_lvl+0x4a/0x63

dump_stack+0x10/0x16

ubsan_epilogue+0x9/0x36

__ubsan_handle_shift_out_of_bounds.cold+0x61/0x10e

? __const_udelay+0x43/0x50

ena_delay_exponential_backoff_us.cold+0x16/0x1e [ena]

wait_for_reset_state+0x54/0xa0 [ena]

ena_com_dev_reset+0xc8/0x110 [ena]

ena_down+0x3fe/0x480 [ena]

ena_destroy_device+0xeb/0xf0 [ena]

ena_fw_reset_device+0x30/0x50 [ena]

process_one_work+0x22b/0x3d0

worker_thread+0x4d/0x3f0

? process_one_work+0x3d0/0x3d0

kthread+0x12a/0x150

? set_kthread_struct+0x50/0x50

ret_from_fork+0x22/0x30

</TASK>

Apparently, the reset delays are getting so large they can trigger a

UBSAN panic.

Looking at the code, the current timeout is capped at 5000us. Using a

base value of 100us, the current code will overflow after (1<<29). Even

at values before 32, this function wraps around, perhaps

unintentionally.

Cap the value of the exponent used for this backoff at (1<<16) which is

larger than currently necessary, but large enough to support bigger

values in the future.