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authorRoss Zwisler <ross.zwisler@linux.intel.com>2017-09-06 16:18:54 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-09-06 17:27:24 -0700
commita2e050f5a9a9bd2b632d67bd06d87088e6a02dae (patch)
treea7cc6d57eccb6b9e168c51ff5d1baf065f62dae7
parent527b19d0808e75fbba896beb2435c2b4d6bcd32a (diff)
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 <ross.zwisler@linux.intel.com> Reviewed-by: Jan Kara <jack@suse.cz> Cc: Christoph Hellwig <hch@lst.de> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Matthew Wilcox <mawilcox@microsoft.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/dax.c5
1 files changed, 5 insertions, 0 deletions
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);