[PATCH] HID: core: check field offset before dumping input

[Deepanshu Kartikey <kartikey406@gmail.com>]

hid_set_field() passes field->usage + offset to hid_dump_input() before
validating offset against field->report_count. field->usage is allocated
with exactly report_count entries, so a larger offset is read out of
bounds before the existing check rejects it:

  BUG: KASAN: slab-out-of-bounds in hid_dump_input+0xcb/0xd0
  Read of size 4 at addr ffff88802ab28fc0 by task kworker/1:2/48

Move the bounds check above the hid_dump_input() call so the function
returns before the dereference.

Reported-by: syzbot+a942efa43c928a1e3daa@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=a942efa43c928a1e3daa
Tested-by: syzbot+a942efa43c928a1e3daa@syzkaller.appspotmail.com
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
 drivers/hid/hid-core.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
index cf123347a2af..7ea1fb62b9d4 100644
--- a/drivers/hid/hid-core.c
+++ b/drivers/hid/hid-core.c
@@ -1933,13 +1933,14 @@ int hid_set_field(struct hid_field *field, unsigned offset, __s32 value)
 
 	size = field->report_size;
 
-	hid_dump_input(field->report->device, field->usage + offset, value);
-
 	if (offset >= field->report_count) {
 		hid_err(field->report->device, "offset (%d) exceeds report_count (%d)\n",
 				offset, field->report_count);
 		return -1;
 	}
+
+	hid_dump_input(field->report->device, field->usage + offset, value);
+
 	if (field->logical_minimum < 0) {
 		if (value != snto32(s32ton(value, size), size)) {
 			hid_err(field->report->device, "value %d is out of range\n", value);
-- 
2.43.0