In the Linux kernel, the following vulnerability has been resolved: HID: core: fix OOB read of field->usage in hid_set_field() hid_set_fie

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

HID: core: fix OOB read of field->usage in hid_set_field()

hid_set_field() hands field->usage + offset to hid_dump_input() before
the guard that bounds offset:

 1hid_dump_input(field->report->device, field->usage + offset, value);
 2 
 3if (offset >= field->report_count) {
 4	hid_err(...);
 5	return -1;
 6}

Under CONFIG_DEBUG_FS hid_dump_input() dereferences that pointer, with
buf = hid_resolv_usage(usage->hid, NULL). The usage[] array is
allocated inline with the hid_field in hid_register_field() and holds
field->maxusage entries, so an offset past it reads off the end of the
kvzalloc()ed allocation and into a neighbouring object. Had the guard
run first, offset < report_count <= maxusage would already have confined
the pointer to the array.

A caller supplies such an offset today. picolcd_fb_send_tile()
validates only report->maxfield before issuing
hid_set_field(report->field[0], 11 + i, ...) for i = 0..31, so its
offsets are fixed at 11..42 and are never checked against the bound
field. When the device registers that field with fewer usages, the
framebuffer deferred-io work drives the read on every tile. KASAN
reports a 4-byte slab-out-of-bounds read in hid_dump_input() below
hid_set_field(), and the same boot logs "offset (1) exceeds
report_count (1)" from the guard that runs only afterwards.

Move the hid_dump_input() call below the guard. Because
field->maxusage >= field->report_count, the guard then establishes that
field->usage + offset lies inside the array before it is dereferenced,
for every caller and without changing behaviour on the valid path.

Discovered by XBOW, triaged by Baul Lee baul.lee@xbow.com