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comedi: Fail COMEDI_INSNLIST ioctl if n_insns is too large

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[ 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: ed9eccbe89 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ian Abbott 2025-07-28 13:18:20 +01:00 • committed by Greg Kroah-Hartman
commit 454d732dfd
2 changed files with 16 additions and 0 deletions
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3
drivers/staging/comedi/comedi_compat32.c
View file

@ -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]));

13
drivers/staging/comedi/comedi_fops.c
View file

@ -1519,6 +1519,16 @@ out:
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
@ -1551,6 +1561,9 @@ 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;