The handling of the `COMEDI_INSNLIST` ioctl allocates a kernel buffer to hold the array of `struct comedi_insn`, getting the length from the `n_insns` member of the `struct comedi_insnlist` supplied by the user. The allocation will fail with a WARNING and a stack dump if it is too large.

Avoid that by failing with an `-EINVAL` error if the supplied `n_insns` value is unreasonable.

Define the limit on the `n_insns` value in the `MAX_INSNS` macro. Set this to the same value as `MAX_SAMPLES` (65536), which is the maximum allowed sum of the values of the member `n` in the array of `struct comedi_insn`, and sensible comedi instructions will have an `n` of at least 1.

Reported-by: syzbot+d6995b62e5ac7d79557a@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=d6995b62e5ac7d79557a Fixes: ed9eccbe8970 ("Staging: add comedi core") Tested-by: Ian Abbott abbotti@mev.co.uk Cc: stable@vger.kernel.org # 5.13+ Signed-off-by: Ian Abbott abbotti@mev.co.uk --- Patch does not apply cleanly to longterm kernels 5.4.x and 5.10.x. --- drivers/comedi/comedi_fops.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+)

diff --git a/drivers/comedi/comedi_fops.c b/drivers/comedi/comedi_fops.c index 3383a7ce27ff..962fb9b18a52 100644 --- a/drivers/comedi/comedi_fops.c +++ b/drivers/comedi/comedi_fops.c @@ -1589,6 +1589,16 @@ static int do_insnlist_ioctl(struct comedi_device *dev, return i; }

+#define MAX_INSNS MAX_SAMPLES +static int check_insnlist_len(struct comedi_device *dev, unsigned int n_insns) +{ + if (n_insns > MAX_INSNS) { + dev_dbg(dev->class_dev, "insnlist length too large\n"); + return -EINVAL; + } + return 0; +} + /* * COMEDI_INSN ioctl * synchronous instruction @@ -2239,6 +2249,9 @@ static long comedi_unlocked_ioctl(struct file *file, unsigned int cmd, rc = -EFAULT; break; } + rc = check_insnlist_len(dev, insnlist.n_insns); + if (rc) + break; insns = kcalloc(insnlist.n_insns, sizeof(*insns), GFP_KERNEL); if (!insns) { rc = -ENOMEM; @@ -3142,6 +3155,9 @@ static int compat_insnlist(struct file *file, unsigned long arg) if (copy_from_user(&insnlist32, compat_ptr(arg), sizeof(insnlist32))) return -EFAULT;

+ rc = check_insnlist_len(dev, insnlist32.n_insns); + if (rc) + return rc; insns = kcalloc(insnlist32.n_insns, sizeof(*insns), GFP_KERNEL); if (!insns) return -ENOMEM;