Merge tag 'iomap-6.6-fixes-2' of git://git.kernel.org/pub/scm/fs/xfs/xfs-linux

Pull iomap fixes from Darrick Wong:

 - Return EIO on bad inputs to iomap_to_bh instead of BUGging, to deal
   less poorly with block device io racing with block device resizing

 - Fix a stale page data exposure bug introduced in 6.6-rc1 when
   unsharing a file range that is not in the page cache

* tag 'iomap-6.6-fixes-2' of git://git.kernel.org/pub/scm/fs/xfs/xfs-linux:
  iomap: convert iomap_unshare_iter to use large folios
  iomap: don't skip reading in !uptodate folios when unsharing a range
  iomap: handle error conditions more gracefully in iomap_to_bh

fs/buffer.c

@@ -2011,7 +2011,7 @@ void folio_zero_new_buffers(struct folio *folio, size_t from, size_t to)
 }
 EXPORT_SYMBOL(folio_zero_new_buffers);
 
-static void
+static int
 iomap_to_bh(struct inode *inode, sector_t block, struct buffer_head *bh,
 		const struct iomap *iomap)
 {
@@ -2025,7 +2025,8 @@ iomap_to_bh(struct inode *inode, sector_t block, struct buffer_head *bh,
 	 * current block, then do not map the buffer and let the caller
 	 * handle it.
 	 */
-	BUG_ON(offset >= iomap->offset + iomap->length);
+	if (offset >= iomap->offset + iomap->length)
+		return -EIO;
 
 	switch (iomap->type) {
 	case IOMAP_HOLE:
@@ -2037,7 +2038,7 @@ iomap_to_bh(struct inode *inode, sector_t block, struct buffer_head *bh,
 		if (!buffer_uptodate(bh) ||
 		    (offset >= i_size_read(inode)))
 			set_buffer_new(bh);
-		break;
+		return 0;
 	case IOMAP_DELALLOC:
 		if (!buffer_uptodate(bh) ||
 		    (offset >= i_size_read(inode)))
@@ -2045,7 +2046,7 @@ iomap_to_bh(struct inode *inode, sector_t block, struct buffer_head *bh,
 		set_buffer_uptodate(bh);
 		set_buffer_mapped(bh);
 		set_buffer_delay(bh);
-		break;
+		return 0;
 	case IOMAP_UNWRITTEN:
 		/*
 		 * For unwritten regions, we always need to ensure that regions
@@ -2062,7 +2063,10 @@ iomap_to_bh(struct inode *inode, sector_t block, struct buffer_head *bh,
 		bh->b_blocknr = (iomap->addr + offset - iomap->offset) >>
 				inode->i_blkbits;
 		set_buffer_mapped(bh);
-		break;
+		return 0;
+	default:
+		WARN_ON_ONCE(1);
+		return -EIO;
 	}
 }
 
@@ -2103,13 +2107,12 @@ int __block_write_begin_int(struct folio *folio, loff_t pos, unsigned len,
 			clear_buffer_new(bh);
 		if (!buffer_mapped(bh)) {
 			WARN_ON(bh->b_size != blocksize);
-			if (get_block) {
+			if (get_block)
 				err = get_block(inode, block, bh, 1);
-				if (err)
-					break;
-			} else {
-				iomap_to_bh(inode, block, bh, iomap);
-			}
+			else
+				err = iomap_to_bh(inode, block, bh, iomap);
+			if (err)
+				break;
 
 			if (buffer_new(bh)) {
 				clean_bdev_bh_alias(bh);

fs/iomap/buffered-io.c

@@ -640,11 +640,13 @@ static int __iomap_write_begin(const struct iomap_iter *iter, loff_t pos,
 	size_t poff, plen;
 
 	/*
-	 * If the write completely overlaps the current folio, then
+	 * If the write or zeroing completely overlaps the current folio, then
 	 * entire folio will be dirtied so there is no need for
 	 * per-block state tracking structures to be attached to this folio.
+	 * For the unshare case, we must read in the ondisk contents because we
+	 * are not changing pagecache contents.
 	 */
-	if (pos <= folio_pos(folio) &&
+	if (!(iter->flags & IOMAP_UNSHARE) && pos <= folio_pos(folio) &&
 	    pos + len >= folio_pos(folio) + folio_size(folio))
 		return 0;
 
@@ -1261,7 +1263,6 @@ static loff_t iomap_unshare_iter(struct iomap_iter *iter)
 	const struct iomap *srcmap = iomap_iter_srcmap(iter);
 	loff_t pos = iter->pos;
 	loff_t length = iomap_length(iter);
-	long status = 0;
 	loff_t written = 0;
 
 	/* don't bother with blocks that are not shared to start with */
@@ -1272,28 +1273,33 @@ static loff_t iomap_unshare_iter(struct iomap_iter *iter)
 		return length;
 
 	do {
-		unsigned long offset = offset_in_page(pos);
-		unsigned long bytes = min_t(loff_t, PAGE_SIZE - offset, length);
 		struct folio *folio;
+		int status;
+		size_t offset;
+		size_t bytes = min_t(u64, SIZE_MAX, length);
 
 		status = iomap_write_begin(iter, pos, bytes, &folio);
 		if (unlikely(status))
 			return status;
-		if (iter->iomap.flags & IOMAP_F_STALE)
+		if (iomap->flags & IOMAP_F_STALE)
 			break;
 
-		status = iomap_write_end(iter, pos, bytes, bytes, folio);
-		if (WARN_ON_ONCE(status == 0))
+		offset = offset_in_folio(folio, pos);
+		if (bytes > folio_size(folio) - offset)
+			bytes = folio_size(folio) - offset;
+
+		bytes = iomap_write_end(iter, pos, bytes, bytes, folio);
+		if (WARN_ON_ONCE(bytes == 0))
 			return -EIO;
 
 		cond_resched();
 
-		pos += status;
-		written += status;
-		length -= status;
+		pos += bytes;
+		written += bytes;
+		length -= bytes;
 
 		balance_dirty_pages_ratelimited(iter->inode->i_mapping);
-	} while (length);
+	} while (length > 0);
 
 	return written;
 }