Affected: Linux

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

usb-storage: alauda: Fix uninit-value in alauda_check_media()

Syzbot got KMSAN to complain about access to an uninitialized value in the alauda subdriver of usb-storage:

BUG: KMSAN: uninit-value in alauda_transport+0x462/0x57f0 drivers/usb/storage/alauda.c:1137 CPU: 0 PID: 12279 Comm: usb-storage Not tainted 5.3.0-rc7+ #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x191/0x1f0 lib/dump_stack.c:113 kmsan_report+0x13a/0x2b0 mm/kmsan/kmsan_report.c:108 __msan_warning+0x73/0xe0 mm/kmsan/kmsan_instr.c:250 alauda_check_media+0x344/0x3310 drivers/usb/storage/alauda.c:460

The problem is that alauda_check_media() doesn't verify that its USB transfer succeeded before trying to use the received data. What should happen if the transfer fails isn't entirely clear, but a reasonably conservative approach is to pretend that no media is present.

A similar problem exists in a usb_stor_dbg() call in alauda_get_media_status(). In this case, when an error occurs the call is redundant, because usb_stor_ctrl_transfer() already will print a debugging message.

Finally, unrelated to the uninitialized memory access, is the fact that alauda_check_media() performs DMA to a buffer on the stack. Fortunately usb-storage provides a general purpose DMA-able buffer for uses like this. We'll use it instead.