From a2e050f5a9a9bd2b632d67bd06d87088e6a02dae Mon Sep 17 00:00:00 2001 From: Ross Zwisler Date: Wed, 6 Sep 2017 16:18:54 -0700 Subject: [PATCH] dax: explain how read(2)/write(2) addresses are validated 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. Link: http://lkml.kernel.org/r/20170816173615.10098-1-ross.zwisler@linux.intel.com Signed-off-by: Ross Zwisler Reviewed-by: Jan Kara Cc: Christoph Hellwig Cc: Dan Williams Cc: Matthew Wilcox Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/dax.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/fs/dax.c b/fs/dax.c index c576f6181dc8..5b2eac3ef077 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -1004,6 +1004,11 @@ 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); -- 2.20.1