btrfs: tree-checker: Check if the file extent end overflows

Under certain conditions, we could have strange file extent item in log
tree like:

  item 18 key (69599 108 397312) itemoff 15208 itemsize 53
	extent data disk bytenr 0 nr 0
	extent data offset 0 nr 18446744073709547520 ram 18446744073709547520

The num_bytes + ram_bytes overflow 64 bit type.

For num_bytes part, we can detect such overflow along with file offset
(key->offset), as file_offset + num_bytes should never go beyond u64.

For ram_bytes part, it's about the decompressed size of the extent, not
directly related to the size.
In theory it is OK to have a large value, and put extra limitation
on RAM bytes may cause unexpected false alerts.

So in tree-checker, we only check if the file offset and num bytes
overflow.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/fs/btrfs/tree-checker.c b/fs/btrfs/tree-checker.c
index 96fce4bef4e7..ccd5706199d7 100644
--- a/fs/btrfs/tree-checker.c
+++ b/fs/btrfs/tree-checker.c
@@ -132,6 +132,7 @@ static int check_extent_data_item(struct extent_buffer *leaf,
         struct btrfs_file_extent_item *fi;
         u32 sectorsize = fs_info->sectorsize;
         u32 item_size = btrfs_item_size_nr(leaf, slot);
+        u64 extent_end;
 
         if (!IS_ALIGNED(key->offset, sectorsize)) {
                 file_extent_err(leaf, slot,
@@ -207,6 +208,16 @@ static int check_extent_data_item(struct extent_buffer *leaf,
             CHECK_FE_ALIGNED(leaf, slot, fi, num_bytes, sectorsize))
                 return -EUCLEAN;
 
+        /* Catch extent end overflow */
+        if (check_add_overflow(btrfs_file_extent_num_bytes(leaf, fi),
+                               key->offset, &extent_end)) {
+                file_extent_err(leaf, slot,
+        "extent end overflow, have file offset %llu extent num bytes %llu",
+                                key->offset,
+                                btrfs_file_extent_num_bytes(leaf, fi));
+                return -EUCLEAN;
+        }
+
         /*
          * Check that no two consecutive file extent items, in the same leaf,
          * present ranges that overlap each other.