[ Upstream commit 08ae4b20f5e82101d77326ecab9089e110f224cc ]

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 Link: https://lore.kernel.org/r/20250704120405.83028-1-abbotti@mev.co.uk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org [ Reworked for before commit bac42fb21259 ("comedi: get rid of compat_alloc_user_space() mess in COMEDI_CMD{,TEST} compat") ] Signed-off-by: Ian Abbott abbotti@mev.co.uk --- v2: Fixed a build error due to applying a fixup to the wrong commit. --- drivers/staging/comedi/comedi_compat32.c | 3 +++ drivers/staging/comedi/comedi_fops.c | 13 +++++++++++++ 2 files changed, 16 insertions(+)

diff --git a/drivers/staging/comedi/comedi_compat32.c b/drivers/staging/comedi/comedi_compat32.c index 36a3564ba1fb..2f444e2b92c2 100644 --- a/drivers/staging/comedi/comedi_compat32.c +++ b/drivers/staging/comedi/comedi_compat32.c @@ -360,6 +360,9 @@ static int compat_insnlist(struct file *file, unsigned long arg) if (err) return -EFAULT;

+ if (n_insns > 65536) /* See MAX_INSNS in comedi_fops.c */ + return -EINVAL; + /* Allocate user memory to copy insnlist and insns into. */ s = compat_alloc_user_space(offsetof(struct combined_insnlist, insn[n_insns])); diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c index 8b2337f8303d..45e868badee4 100644 --- a/drivers/staging/comedi/comedi_fops.c +++ b/drivers/staging/comedi/comedi_fops.c @@ -1502,6 +1502,16 @@ static int parse_insn(struct comedi_device *dev, struct comedi_insn *insn, return ret; }

+#define MAX_INSNS 65536 +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_INSNLIST ioctl * synchronous instruction list @@ -1534,6 +1544,9 @@ static int do_insnlist_ioctl(struct comedi_device *dev, if (copy_from_user(&insnlist, arg, sizeof(insnlist))) return -EFAULT;

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