[PATCH v4 3/5] btrfs: check verity for reads of inline extents and holes

[Boris Burkov <boris@bur.io>]

The majority of reads receive a verity check after the bio is complete
as the page is marked uptodate. However, there is a class of reads which
are handled with btrfs logic in readpage, rather than by submitting a
bio. Specifically, these are inline extents, preallocated extents, and
holes. Tweak readpage so that if it is going to mark such a page
uptodate, it first checks verity on it.

Now if a veritied file has corruption to this class of EXTENT_DATA
items, it will be detected at read time.

There is one annoying edge case that requires checking for start <
last_byte: if userspace reads to the end of a file with page aligned
size and then tries to keep reading (as cat does), the buffered read
code will try to read the page past the end of the file, and expects it
to be filled with 0s and marked uptodate. That bogus page is not part of
the data hashed by verity, so we have to ignore it.

Signed-off-by: Boris Burkov <boris@bur.io>
---
 fs/btrfs/extent_io.c | 26 +++++++-------------------
 1 file changed, 7 insertions(+), 19 deletions(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index d1f57a4ad2fb..d1493a876915 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -2202,18 +2202,6 @@ int test_range_bit(struct extent_io_tree *tree, u64 start, u64 end,
 	return bitset;
 }
 
-/*
- * helper function to set a given page up to date if all the
- * extents in the tree for that page are up to date
- */
-static void check_page_uptodate(struct extent_io_tree *tree, struct page *page)
-{
-	u64 start = page_offset(page);
-	u64 end = start + PAGE_SIZE - 1;
-	if (test_range_bit(tree, start, end, EXTENT_UPTODATE, 1, NULL))
-		SetPageUptodate(page);
-}
-
 int free_io_failure(struct extent_io_tree *failure_tree,
 		    struct extent_io_tree *io_tree,
 		    struct io_failure_record *rec)
@@ -3467,14 +3455,14 @@ int btrfs_do_readpage(struct page *page, struct extent_map **em_cached,
 					    &cached, GFP_NOFS);
 			unlock_extent_cached(tree, cur,
 					     cur + iosize - 1, &cached);
-			end_page_read(page, true, cur, iosize);
+			ret = end_page_read(page, true, cur, iosize);
 			break;
 		}
 		em = __get_extent_map(inode, page, pg_offset, cur,
 				      end - cur + 1, em_cached);
 		if (IS_ERR_OR_NULL(em)) {
 			unlock_extent(tree, cur, end);
-			end_page_read(page, false, cur, end + 1 - cur);
+			ret = end_page_read(page, false, cur, end + 1 - cur);
 			break;
 		}
 		extent_offset = cur - em->start;
@@ -3555,9 +3543,10 @@ int btrfs_do_readpage(struct page *page, struct extent_map **em_cached,
 
 			set_extent_uptodate(tree, cur, cur + iosize - 1,
 					    &cached, GFP_NOFS);
+
 			unlock_extent_cached(tree, cur,
 					     cur + iosize - 1, &cached);
-			end_page_read(page, true, cur, iosize);
+			ret = end_page_read(page, true, cur, iosize);
 			cur = cur + iosize;
 			pg_offset += iosize;
 			continue;
@@ -3565,9 +3554,8 @@ int btrfs_do_readpage(struct page *page, struct extent_map **em_cached,
 		/* the get_extent function already copied into the page */
 		if (test_range_bit(tree, cur, cur_end,
 				   EXTENT_UPTODATE, 1, NULL)) {
-			check_page_uptodate(tree, page);
 			unlock_extent(tree, cur, cur + iosize - 1);
-			end_page_read(page, true, cur, iosize);
+			ret = end_page_read(page, true, cur, iosize);
 			cur = cur + iosize;
 			pg_offset += iosize;
 			continue;
@@ -3577,7 +3565,7 @@ int btrfs_do_readpage(struct page *page, struct extent_map **em_cached,
 		 */
 		if (block_start == EXTENT_MAP_INLINE) {
 			unlock_extent(tree, cur, cur + iosize - 1);
-			end_page_read(page, false, cur, iosize);
+			ret = end_page_read(page, false, cur, iosize);
 			cur = cur + iosize;
 			pg_offset += iosize;
 			continue;
@@ -3595,7 +3583,7 @@ int btrfs_do_readpage(struct page *page, struct extent_map **em_cached,
 			*bio_flags = this_bio_flag;
 		} else {
 			unlock_extent(tree, cur, cur + iosize - 1);
-			end_page_read(page, false, cur, iosize);
+			ret = end_page_read(page, false, cur, iosize);
 			goto out;
 		}
 		cur = cur + iosize;
-- 
2.30.2