btrfs: ref-verify: handle damaged extent root tree

Syzbot hits a problem with enabled ref-verify, ignorebadroots and a
fuzzed/damaged extent tree. There's no fallback option like in other
places that can deal with it so disable the whole ref-verify as it is
just a debugging feature.

Reported-by: syzbot+9c3e0cdfbfe351b0bc0e@syzkaller.appspotmail.com
Link: https://lore.kernel.org/all/0000000000001b6052062139be1c@google.com/
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/ref-verify.c b/fs/btrfs/ref-verify.c
index 3871c3a6c743b511a5c6cb0d4ccf48f2bffa5c5c..9f1858b42c0e212abaf78b2cdf0c295e03aa9265 100644 (file)
--- a/fs/btrfs/ref-verify.c
+++ b/fs/btrfs/ref-verify.c
@@ -980,11 +980,18 @@ int btrfs_build_ref_tree(struct btrfs_fs_info *fs_info)
        if (!btrfs_test_opt(fs_info, REF_VERIFY))
                return 0;
 
+       extent_root = btrfs_extent_root(fs_info, 0);
+       /* If the extent tree is damaged we cannot ignore it (IGNOREBADROOTS). */
+       if (IS_ERR(extent_root)) {
+               btrfs_warn(fs_info, "ref-verify: extent tree not available, disabling");
+               btrfs_clear_opt(fs_info->mount_opt, REF_VERIFY);
+               return 0;
+       }
+
        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;
 
-       extent_root = btrfs_extent_root(fs_info, 0);
        eb = btrfs_read_lock_root_node(extent_root);
        level = btrfs_header_level(eb);
        path->nodes[level] = eb;