Add a comment explaining how the user addresses provided to read(2) and write(2) are validated in the DAX I/O path. We call dax_copy_from_iter() or copy_to_iter() on these without calling access_ok() first in the DAX code, and there was a concern that the user might be able to read/write to arbitrary kernel addresses with this path. Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> --- Adding a comment instead of adding redundant access_ok() calls in the DAX code. If this is the wrong path to take, please let me know. fs/dax.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/fs/dax.c b/fs/dax.c index 8c67517..2d50f32 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -1060,6 +1060,11 @@ dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data, if (map_len > end - pos) map_len = end - pos; + /* + * The userspace address for the memory copy has already been + * validated via access_ok() in either vfs_read() or + * vfs_write(), depending on which operation we are doing. + */ if (iov_iter_rw(iter) == WRITE) map_len = dax_copy_from_iter(dax_dev, pgoff, kaddr, map_len, iter); -- 2.9.5
