[PATCH v2] comedi: Fix memory leak in compat_insnlist()

[Ian Abbott <abbotti@mev.co.uk>]

`compat_insnlist()` handles the 32-bit version of the `COMEDI_INSNLIST`
ioctl (whenwhen `CONFIG_COMPAT` is enabled).  It allocates memory to
temporarily hold an array of `struct comedi_insn` converted from the
32-bit version in user space.  This memory is only being freed if there
is a fault while filling the array, otherwise it is leaked.

Add a call to `kfree()` to fix the leak.

Fixes: b8d47d881305 ("comedi: get rid of compat_alloc_user_space() mess in COMEDI_INSNLIST compat"
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-staging@lists.linux.dev
Cc: <stable@vger.kernel.org> # 5.13+
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
---
v2: Corrected typo in Greg's email address.

N.B. Also need patches for 5.8+ from before comedi moved out of staging.
---
 drivers/comedi/comedi_fops.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/comedi/comedi_fops.c b/drivers/comedi/comedi_fops.c
index df77b6bf5c64..763cea8418f8 100644
--- a/drivers/comedi/comedi_fops.c
+++ b/drivers/comedi/comedi_fops.c
@@ -3090,6 +3090,7 @@ static int compat_insnlist(struct file *file, unsigned long arg)
 	mutex_lock(&dev->mutex);
 	rc = do_insnlist_ioctl(dev, insns, insnlist32.n_insns, file);
 	mutex_unlock(&dev->mutex);
+	kfree(insns);
 	return rc;
 }
 
-- 
2.33.0