From: Mathias Krause minipli@grsecurity.net
commit c72ea20503610a4a7ba26c769357d31602769c01 upstream.
If we fail to copy the just created file descriptor to userland, we try to clean up by putting back 'fd' and freeing 'ib'. The code uses put_unused_fd() for the former which is wrong, as the file descriptor was already published by fd_install() which gets called internally by anon_inode_getfd().
This makes the error handling code leaving a half cleaned up file descriptor table around and a partially destructed 'file' object, allowing userland to play use-after-free tricks on us, by abusing the still usable fd and making the code operate on a dangling 'file->private_data' pointer.
Instead of leaving the kernel in a partially corrupted state, don't attempt to explicitly clean up and leave this to the process exit path that'll release any still valid fds, including the one created by the previous call to anon_inode_getfd(). Simply return -EFAULT to indicate the error.
Fixes: f73f7f4da581 ("iio: buffer: add ioctl() to support opening extra buffers for IIO device") Cc: stable@kernel.org Cc: Jonathan Cameron jic23@kernel.org Cc: Alexandru Ardelean ardeleanalex@gmail.com Cc: Lars-Peter Clausen lars@metafoo.de Cc: Nuno Sa Nuno.Sa@analog.com Reported-by: Dan Carpenter dan.carpenter@oracle.com Signed-off-by: Mathias Krause minipli@grsecurity.net Reviewed-by: Jonathan Cameron Jonathan.Cameron@huawei.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/iio/industrialio-buffer.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-)
--- a/drivers/iio/industrialio-buffer.c +++ b/drivers/iio/industrialio-buffer.c @@ -1569,9 +1569,17 @@ static long iio_device_buffer_getfd(stru }
if (copy_to_user(ival, &fd, sizeof(fd))) { - put_unused_fd(fd); - ret = -EFAULT; - goto error_free_ib; + /* + * "Leak" the fd, as there's not much we can do about this + * anyway. 'fd' might have been closed already, as + * anon_inode_getfd() called fd_install() on it, which made + * it reachable by userland. + * + * Instead of allowing a malicious user to play tricks with + * us, rely on the process exit path to do any necessary + * cleanup, as in releasing the file, if still needed. + */ + return -EFAULT; }
return 0;