6.11-stable review patch. If anyone has any objections, please let me know.
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From: Darrick J. Wong djwong@kernel.org
[ Upstream commit 50793801fc7f6d08def48754fb0f0706b0cfc394 ]
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: d984648e428b ("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@fr... Reviewed-by: Christoph Hellwig hch@lst.de Signed-off-by: Christian Brauner brauner@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- fs/dax.c | 34 +++++++++++++++++++++++++++------- 1 file changed, 27 insertions(+), 7 deletions(-)
diff --git a/fs/dax.c b/fs/dax.c index 9fbbdaa784b43..21b47402b3dca 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;