tree 7b482dcaa4b4db142fcabfe866ebe9a7829e7148
parent f6c23f483937b8be53f313ec31068acdca91a25d
author Lars-Peter Clausen <lars@metafoo.de> 1381825800 +0100
committer Jonathan Cameron <jic23@kernel.org> 1381861162 +0100

iio:kfifo: Protect against concurrent access from userspace

It is possible for userspace to concurrently access the buffer from multiple
threads or processes. To avoid corruption of the internal state of the buffer we
need to add proper locking. It is possible for multiple processes to try to read
from the buffer concurrently and it is also possible that one process causes a
buffer re-allocation while a different process still access the buffer. Both can
be fixed by protecting the calls to kfifo_to_user() and kfifo_alloc() by the
same mutex. In iio_read_first_n_kfifo() we also use kfifo_recsize() instead of
the buffers bytes_per_datum to avoid a race that can happen if bytes_per_datum
has been changed, but the buffer has not been reallocated yet.

Note that all access to the buffer from within the kernel is already properly
synchronized, so there is no need for extra locking in iio_store_to_kfifo().

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>