The comedi_buf_munge() function performs a modulo operation `async->munge_chan %= async->cmd.chanlist_len` without first checking if chanlist_len is zero. If a user program submits a command with chanlist_len set to zero, this causes a divide-by-zero error when the device processes data in the interrupt handler path.

Add a check for zero chanlist_len at the beginning of the function, similar to the existing checks for !map and CMDF_RAWDATA flag. When chanlist_len is zero, update munge_count and return early, indicating the data was handled without munging.

This prevents potential kernel panics from malformed user commands.

Reported-by: syzbot+f6c3c066162d2c43a66c@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=f6c3c066162d2c43a66c Cc: stable@vger.kernel.org Signed-off-by: Deepanshu Kartikey kartikey406@gmail.com --- drivers/comedi/comedi_buf.c | 5 +++++ 1 file changed, 5 insertions(+)

diff --git a/drivers/comedi/comedi_buf.c b/drivers/comedi/comedi_buf.c index 002c0e76baff..786f888299ce 100644 --- a/drivers/comedi/comedi_buf.c +++ b/drivers/comedi/comedi_buf.c @@ -321,6 +321,11 @@ static unsigned int comedi_buf_munge(struct comedi_subdevice *s, async->munge_count += num_bytes; return num_bytes; } + + if (async->cmd.chanlist_len == 0) { + async->munge_count += num_bytes; + return num_bytes; + }

/* don't munge partial samples */ num_bytes -= num_bytes % num_sample_bytes;