The compat handler for ioctls to the virtual nci device is missing. So, nci-specific ioctls of a compat task return with -1 and errno set to ENOTTY. Add a handler. The handling of an ioctl() call of a compat task to get the index of virtual nci device (IOCTL_GET_NCIDEV_IDX) lands in the default case of the ioctl compat handler (see fs/ioctl.c): COMPAT_SYSCALL_DEFINE3(ioctl, ...) { ... default: error = do_vfs_ioctl(fd_file(f), fd, cmd, ...); if (error != -ENOIOCTLCMD) break; if (fd_file(f)->f_op->compat_ioctl) error = fd_file(f)->f_op->compat_ioctl(fd_file(f), cmd, arg); if (error == -ENOIOCTLCMD) error = -ENOTTY; ... } There, do_vfs_ioctl() returns -ENOIOCTLCMD and compat_ioctl is not set for virtual_ncidev_fops, i.e. f_op->compat_ioctl == NULL. So, the ioctl() syscall returns with -1 and errno set to ENOTTY to the compat task. To fix this, use the compat_ptr_ioctl helper for compat handling here. It shall be used for ioctls that "either ignore the argument or pass a pointer to a compatible data type". The driver's sole ioctl takes a user void pointer and copies nfc_dev->idx to it, a 4-byte integer across all ABIs. This issue has been found by running the nci_dev kernel selftest as rv64 binary on top of a CHERI kernel, where the ioctl() ends up in the ioctl compat handler, similar to a 32-bit application on top of a 64-bit kernel. Fixes: e624e6c3e777 ("nfc: Add a virtual nci device driver") Signed-off-by: Chris Gellermann --- drivers/nfc/virtual_ncidev.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/nfc/virtual_ncidev.c b/drivers/nfc/virtual_ncidev.c index 8eeb447ac96e..e51c647b27eb 100644 --- a/drivers/nfc/virtual_ncidev.c +++ b/drivers/nfc/virtual_ncidev.c @@ -195,7 +195,8 @@ static const struct file_operations virtual_ncidev_fops = { .write = virtual_ncidev_write, .open = virtual_ncidev_open, .release = virtual_ncidev_close, - .unlocked_ioctl = virtual_ncidev_ioctl + .unlocked_ioctl = virtual_ncidev_ioctl, + .compat_ioctl = compat_ptr_ioctl, }; static struct miscdevice miscdev = { -- 2.47.3