The patch titled
Subject: dax: explain how read(2)/write(2) addresses are validated
has been added to the -mm tree. Its filename is
dax-explain-how-read2-write2-addresses-are-validated.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/dax-explain-how-read2-write2-addresses-are-validated.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/dax-explain-how-read2-write2-addresses-are-validated.patch
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------------------------------------------------------
From: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Subject: 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@xxxxxxxxxxxxxxx
Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/dax.c | 5 +++++
1 file changed, 5 insertions(+)
diff -puN fs/dax.c~dax-explain-how-read2-write2-addresses-are-validated fs/dax.c
--- a/fs/dax.c~dax-explain-how-read2-write2-addresses-are-validated
+++ a/fs/dax.c
@@ -1001,6 +1001,11 @@ dax_iomap_actor(struct inode *inode, lof
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);
_
Patches currently in -mm which might be from ross.zwisler@xxxxxxxxxxxxxxx are
mm-add-vm_insert_mixed_mkwrite.patch
dax-relocate-some-dax-functions.patch
dax-use-common-4k-zero-page-for-dax-mmap-reads.patch
dax-remove-dax-code-from-page_cache_tree_insert.patch
dax-move-all-dax-radix-tree-defs-to-fs-daxc.patch
dax-explain-how-read2-write2-addresses-are-validated.patch
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