Re: [PATCH] HID: picolcd: clamp eeprom debugfs read to bytes actually received

[Jiri Kosina]

On Wed, 15 Jul 2026, Ibrahim Hashimov wrote:

> picolcd_debug_eeprom_read() trusts resp->raw_data[2] -- a length byte
> supplied by the device in its REPORT_EE_DATA reply -- clamped only to
> the caller's read() count:
> 
> 	ret = resp->raw_data[2];
> 	if (ret > s)
> 		ret = s;
> 	if (copy_to_user(u, resp->raw_data+3, ret))
> 
> It never checks resp->raw_size, the number of bytes picolcd_raw_event()
> actually copied into the 64-byte raw_data[] of the kmalloc'd struct
> picolcd_pending. A device (or a spoofed picoLCD) returning a length byte
> of 0xff, read with a count >= 255, makes copy_to_user() read past
> raw_data[] into adjacent slab memory and return it to userspace through
> the debugfs "eeprom" file:
> 
> 	BUG: KASAN: slab-out-of-bounds in _copy_to_user
> 	Read of size 255 ... picolcd_debug_eeprom_read+0x214/0x2f0 [hid_picolcd]
> 
> The debug-dump path in the same file already validates the device length
> byte against the received size before trusting it; this read does not.
> The file is created S_IRUSR (root-only) and a crafted device is needed,
> so it is neither unprivileged- nor remotely-triggerable.
> 
> Clamp the copy length to resp->raw_size - 3 (the payload actually
> received, minus the 3-byte header), floored at 0 for short replies.
> 
> Fixes: 9bbf2b98ba11 ("HID: add experimental access to PicoLCD device's EEPROM and FLASH")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Ibrahim Hashimov <security@xxxxxxxxxxxx>
> Assisted-by: AuditCode-AI:2026.07

Applied, thanks.

-- 
Jiri Kosina
SUSE Labs