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fsdax: dax_unshare_iter needs to copy entire blocks

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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@fujitsu.com
Fixes: d984648e42 ("fsdax,xfs: port unshare to fsdax")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Link: https://lore.kernel.org/r/172796813328.1131942.16777025316348797355.stgit@frogsfrogsfrogs
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Darrick J. Wong 2024-10-03 08:09:48 -07:00 committed by Christian Brauner
parent 95472274b6
commit 50793801fc
No known key found for this signature in database
GPG Key ID: 91C61BC06578DCA2
1 changed files with 27 additions and 7 deletions
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34
fs/dax.c
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@ -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;