Re: [PATCH] btrfs: add a sanity check for btrfs root in btrfs_search_old_slot()

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

在 2025/2/24 18:21, Ma Ke 写道:
> When searching the extent tree to gather the needed extent info,
> btrfs_search_old_slot() doesn't check if the target root is NULL or
> not, resulting the null-ptr-deref. Add sanity check for btrfs root
> before using it in btrfs_search_old_slot().

I do not think it's the case anymore.

Commit 6aecd91a5c5b ("btrfs: avoid NULL pointer dereference if no valid
extent tree") has introduced a check for the extent root, at the very
beginning of scrub_find_fill_first_stripe().

Thus it will never call find_first_extent_item() to search the NULL
extent tree.

Or do you have another case where we need to search extent tree
meanwhile the fs is mounted with rescue=ibadroots?

Thanks,
Qu

>
> Found by code review.
>
> Cc: stable@vger.kernel.org
> Fixes: 0b246afa62b0 ("btrfs: root->fs_info cleanup, add fs_info convenience variables")
> Signed-off-by: Ma Ke <make24@iscas.ac.cn>
> ---
>   fs/btrfs/ctree.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
> index 3dc5a35dd19b..4e2e1c38d33a 100644
> --- a/fs/btrfs/ctree.c
> +++ b/fs/btrfs/ctree.c
> @@ -2232,7 +2232,7 @@ ALLOW_ERROR_INJECTION(btrfs_search_slot, ERRNO);
>   int btrfs_search_old_slot(struct btrfs_root *root, const struct btrfs_key *key,
>   			  struct btrfs_path *p, u64 time_seq)
>   {
> -	struct btrfs_fs_info *fs_info = root->fs_info;
> +	struct btrfs_fs_info *fs_info;
>   	struct extent_buffer *b;
>   	int slot;
>   	int ret;
> @@ -2241,6 +2241,10 @@ int btrfs_search_old_slot(struct btrfs_root *root, const struct btrfs_key *key,
>   	int lowest_unlock = 1;
>   	u8 lowest_level = 0;
>
> +	if (!root)
> +		return -EINVAL;
> +
> +	fs_info = root->fs_info;
>   	lowest_level = p->lowest_level;
>   	WARN_ON(p->nodes[0] != NULL);
>   	ASSERT(!p->nowait);