btrfs: scrub: limit RST scrub to chunk boundary

[BUG]
If there is an extent beyond chunk boundary, currently RST scrub would
error out.

[CAUSE]
In scrub_submit_extent_sector_read(), we completely rely on
extent_sector_bitmap, which is populated using extent tree.

The extent tree can be corrupted that there is an extent item beyond a
chunk.

In that case, RST scrub would fail and error out.

[FIX]
Despite the extent_sector_bitmap usage, also limit the read to chunk
boundary.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/scrub.c

@@ -1646,6 +1646,9 @@ static void scrub_submit_extent_sector_read(struct scrub_ctx *sctx,
 {
 	struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
 	struct btrfs_bio *bbio = NULL;
+	unsigned int nr_sectors = min(BTRFS_STRIPE_LEN, stripe->bg->start +
+				      stripe->bg->length - stripe->logical) >>
+				  fs_info->sectorsize_bits;
 	u64 stripe_len = BTRFS_STRIPE_LEN;
 	int mirror = stripe->mirror_num;
 	int i;
@@ -1656,6 +1659,10 @@ static void scrub_submit_extent_sector_read(struct scrub_ctx *sctx,
 		struct page *page = scrub_stripe_get_page(stripe, i);
 		unsigned int pgoff = scrub_stripe_get_page_offset(stripe, i);
 
+		/* We're beyond the chunk boundary, no need to read anymore. */
+		if (i >= nr_sectors)
+			break;
+
 		/* The current sector cannot be merged, submit the bio. */
 		if (bbio &&
 		    ((i > 0 &&