From: Deepanshu Kartikey Date: Wed, 24 Sep 2025 10:26:39 +0000 (+0530) Subject: comedi: fix divide-by-zero in comedi_buf_munge() X-Git-Tag: v6.12.56~16 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=a4bb5d1bc2f238461bcbe5303eb500466690bb2c;p=thirdparty%2Fkernel%2Fstable.git comedi: fix divide-by-zero in comedi_buf_munge() commit 87b318ba81dda2ee7b603f4f6c55e78ec3e95974 upstream. 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 Reviewed-by: Ian Abbott Link: https://patch.msgid.link/20250924102639.1256191-1-kartikey406@gmail.com Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/comedi/comedi_buf.c b/drivers/comedi/comedi_buf.c index 393966c09740..ef38e9ad98f6 100644 --- a/drivers/comedi/comedi_buf.c +++ b/drivers/comedi/comedi_buf.c @@ -368,7 +368,7 @@ 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; }