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 --- v2: Merged the chanlist_len check with existing early return check as suggested by Ian Abbott
--- drivers/comedi/comedi_buf.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/comedi/comedi_buf.c b/drivers/comedi/comedi_buf.c index 002c0e76baff..c7c262a2d8ca 100644 --- a/drivers/comedi/comedi_buf.c +++ b/drivers/comedi/comedi_buf.c @@ -317,7 +317,7 @@ static unsigned int comedi_buf_munge(struct comedi_subdevice *s, unsigned int count = 0; const unsigned int num_sample_bytes = comedi_bytes_per_sample(s);
- if (!s->munge || (async->cmd.flags & CMDF_RAWDATA)) { + if (!s->munge || (async->cmd.flags & CMDF_RAWDATA) || async->cmd.chanlist_len == 0) { async->munge_count += num_bytes; return num_bytes; }