Input: evdev - sanitize event type index when fetching event masks
In the Linux kernel, the following vulnerability has been resolved:
Input: evdev - sanitize event type index when fetching event masks
The user-supplied event type index passed to EVIOCGMASK / EVIOCSMASK
ioctls is used to index the static counts array in evdev_get_mask_cnt()
and client evmasks array in evdev_get_mask().
While the event type is architecturally bounded by EV_CNT, speculative
execution may mispredict bounds checks and perform out-of-bounds loads.
Sanitize the event type index in evdev_get_mask_cnt() branchlessly using
array_index_mask_nospec(). This clamps the index to 0 for safe array
access and forces the returned count to 0 speculatively when the index
is out of bounds.
We do not need additional array_index_nospec() calls in evdev_get_mask()
because evdev_get_mask_cnt() speculatively forces the count (and
resulting xfer_size) to 0 for out-of-bounds types, preventing any
speculative memory access to client evmasks array.
