ALSA: scarlett2: Allow flash writes ending at segment boundary

scarlett2_hwdep_write() rejects writes when offset + count is greater than
or equal to the selected flash segment size. That incorrectly treats a
write ending exactly at the end of the segment as out of space, although
the last byte written is still within the segment.

Split invalid argument checks from the segment-space check, keep
zero-length writes as no-ops, and compare count against the remaining
segment size. This permits exact-end writes and avoids relying on
offset + count before deciding whether the request is in bounds.

Fixes: 1abfbd3c9527 ("ALSA: scarlett2: Add support for uploading new firmware")
Cc: stable@vger.kernel.org
Signed-off-by: Cássio Gabriel <cassiogabrielcontato@gmail.com>
Link: https://patch.msgid.link/20260519-alsa-scarlett2-flash-write-boundary-v1-1-b550480e92da@gmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/usb/mixer_scarlett2.c b/sound/usb/mixer_scarlett2.c
index 0f83f8981213fba49d2c1e027ca5d7fe436d30f5..8e80a7165faf22c025d9928664c2f829dfa48cca 100644 (file)
--- a/sound/usb/mixer_scarlett2.c
+++ b/sound/usb/mixer_scarlett2.c
@@ -9187,12 +9187,15 @@ static long scarlett2_hwdep_write(struct snd_hwdep *hw,
        flash_size = private->flash_segment_blocks[segment_id] *
                     SCARLETT2_FLASH_BLOCK_SIZE;
 
-       if (count < 0 || *offset < 0 || *offset + count >= flash_size)
-               return -ENOSPC;
+       if (count < 0 || *offset < 0)
+               return -EINVAL;
 
        if (!count)
                return 0;
 
+       if (*offset >= flash_size || count > flash_size - *offset)
+               return -ENOSPC;
+
        /* Limit the *req size to SCARLETT2_FLASH_RW_MAX */
        if (count > max_data_size)
                count = max_data_size;