From: Darrick J. Wong <djwong@xxxxxxxxxx>
The code that copies data from srcmap to iomap in dax_unshare_iter is
very very broken, which bfoster's recent fsx changes have exposed.
If the pos and len passed to dax_file_unshare are not aligned to an
fsblock boundary, the iter pos and length in the _iter function will
reflect this unalignment.
dax_iomap_direct_access always returns a pointer to the start of the
kmapped fsdax page, even if its pos argument is in the middle of that
page. This is catastrophic for data integrity when iter->pos is not
aligned to a page, because daddr/saddr do not point to the same byte in
the file as iter->pos. Hence we corrupt user data by copying it to the
wrong place.
If iter->pos + iomap_length() in the _iter function not aligned to a
page, then we fail to copy a full block, and only partially populate the
destination block. This is catastrophic for data confidentiality
because we expose stale pmem contents.
Fix both of these issues by aligning copy_pos/copy_len to a page
boundary (remember, this is fsdax so 1 fsblock == 1 base page) so that
we always copy full blocks.
We're not done yet -- there's no call to invalidate_inode_pages2_range,
so programs that have the file range mmap'd will continue accessing the
old memory mapping after the file metadata updates have completed.
Be careful with the return value -- if the unshare succeeds, we still
need to return the number of bytes that the iomap iter thinks we're
operating on.
Cc: ruansy.fnst@xxxxxxxxxxx
Fixes: d984648e428b ("fsdax,xfs: port unshare to fsdax")
Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx>
---
fs/dax.c | 34 +++++++++++++++++++++++++++-------
1 file changed, 27 insertions(+), 7 deletions(-)
diff --git a/fs/dax.c b/fs/dax.c
index 9fbbdaa784b4..21b47402b3dc 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1262,26 +1262,46 @@ static s64 dax_unshare_iter(struct iomap_iter *iter)
{
struct iomap *iomap = &iter->iomap;
const struct iomap *srcmap = iomap_iter_srcmap(iter);
- loff_t pos = iter->pos;
- loff_t length = iomap_length(iter);
+ loff_t copy_pos = iter->pos;
+ u64 copy_len = iomap_length(iter);
+ u32 mod;
int id = 0;
s64 ret = 0;
void *daddr = NULL, *saddr = NULL;
if (!iomap_want_unshare_iter(iter))
- return length;
+ return iomap_length(iter);
+
+ /*
+ * Extend the file range to be aligned to fsblock/pagesize, because
+ * we need to copy entire blocks, not just the byte range specified.
+ * Invalidate the mapping because we're about to CoW.
+ */
+ mod = offset_in_page(copy_pos);
+ if (mod) {
+ copy_len += mod;
+ copy_pos -= mod;
+ }
+
+ mod = offset_in_page(copy_pos + copy_len);
+ if (mod)
+ copy_len += PAGE_SIZE - mod;
+
+ invalidate_inode_pages2_range(iter->inode->i_mapping,
+ copy_pos >> PAGE_SHIFT,
+ (copy_pos + copy_len - 1) >> PAGE_SHIFT);
id = dax_read_lock();
- ret = dax_iomap_direct_access(iomap, pos, length, &daddr, NULL);
+ ret = dax_iomap_direct_access(iomap, copy_pos, copy_len, &daddr, NULL);
if (ret < 0)
goto out_unlock;
- ret = dax_iomap_direct_access(srcmap, pos, length, &saddr, NULL);
+ ret = dax_iomap_direct_access(srcmap, copy_pos, copy_len, &saddr, NULL);
if (ret < 0)
goto out_unlock;
- if (copy_mc_to_kernel(daddr, saddr, length) == 0)
- ret = length;
+ if (copy_mc_to_kernel(daddr, saddr, copy_len) == 0)
+ ret = iomap_length(iter);
else
ret = -EIO;
