Re: [PATCH v2] can: usb: f81604: fix struct f81604_int_data size mismatch

[Greg Kroah-Hartman]

On Mon, Aug 24, 2026 at 09:18:14PM +0800, Ji-Ze Hong via B4 Relay wrote:
> From: "Ji-Ze Hong (Peter Hong)" <peter_hong@xxxxxxxxxxxxx>
> 
> The struct f81604_int_data defines 9 bytes of interrupt data:
> - Byte 0: Status register (sr)
> - Byte 1: Interrupt register (isrc)
> - Byte 2: Interrupt enable register (ier)
> - Byte 3: Arbitration lost capture (alc)
> - Byte 4: Error code capture (ecc)
> - Byte 5: Error warning limit register (ewlr)
> - Byte 6: RX error counter (rxerr)
> - Byte 7: TX error counter (txerr)
> - Byte 8: Reserved (val)
> 
> The hardware sends exactly 9 bytes for the interrupt endpoint.
> However, the struct was defined with __aligned(4) attribute which
> caused the compiler to pad the struct to 12 bytes.
> 
> This causes a problem in f81604_read_int_callback() where the short
> URB check compares urb->actual_length against sizeof(*data). When
> sizeof(struct f81604_int_data) is 12 but the hardware only sends 9
> bytes, the check fails and valid interrupt messages are discarded.
> 
> This results in the driver only being able to transmit once because
> the TX complete interrupt is never processed.
> 
> Fix this by removing the __aligned(4) attribute so the struct size
> matches the actual hardware data size of 9 bytes.
> 
> Fixes: 7299b1b39a25 ("can: usb: f81604: handle short interrupt urb messages properly")
> Cc: stable@xxxxxxxxxxxxxxx
> Reported-by: Dynetrex, Admin <admin@xxxxxxxxxxxx>
> Closes: https://lore.kernel.org/all/A3834A07-5639-4779-844F-C5843DFC3928@xxxxxxxxxxxx/
> Signed-off-by: Ji-Ze Hong (Peter Hong) <peter_hong@xxxxxxxxxxxxx>
> ---
> v2:
> - Added Reported-by and Remove mismatched Fixes tags

Acked-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>