On Wed 16-08-17 11:36:15, Ross Zwisler wrote: > 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> Looks OK to me so feel free to add: Reviewed-by: Jan Kara <jack@xxxxxxx> Just I'd note that standard buffered read / write path is no different so I don't see a big point in adding this comment when it is not in any other path either... Honza > --- > > 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 > -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
