linux-kernel - Re: [PATCH] btrfs: add a sanity check for btrfs root

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Message-ID: <03bcaafe-4a15-487a-af2b-b23970162bbb@gmx.com>
Date: Fri, 25 Oct 2024 20:23:07 +1030
From: Qu Wenruo <quwenruo.btrfs@....com>
To: Lizhi Xu <lizhi.xu@...driver.com>,
 syzbot+3030e17bd57a73d39bd7@...kaller.appspotmail.com
Cc: clm@...com, dsterba@...e.com, josef@...icpanda.com,
 linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
 syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH] btrfs: add a sanity check for btrfs root



在 2024/10/25 15:25, Lizhi Xu 写道:
> Syzbot report a null-ptr-deref in btrfs_search_slot.
> It use the input logical can't find the extent root in extent_from_logical,
> and triger the null-ptr-deref in btrfs_search_slot.
> Add sanity check for btrfs root before using it in btrfs_search_slot.

Although I'd prefer to explain a little more about why the NULL root
pointer can happen (caused by the rescue=all mount option), which can
cause NULL root pointer for non-critical tree roots, like
uuid/csum/extent or even device trees.

You don't need to bother sending an update.
I can add such info when pushing to the maintainer's tree.

>
> Reported-by: syzbot+3030e17bd57a73d39bd7@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=3030e17bd57a73d39bd7
> Signed-off-by: Lizhi Xu <lizhi.xu@...driver.com>

Reviewed-by: Qu Wenruo <wqu@...e.com>

Thanks,
Qu
> ---
>   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 0cc919d15b14..9c05cab473f5 100644
> --- a/fs/btrfs/ctree.c
> +++ b/fs/btrfs/ctree.c
> @@ -2010,7 +2010,7 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root,
>   		      const struct btrfs_key *key, struct btrfs_path *p,
>   		      int ins_len, int cow)
>   {
> -	struct btrfs_fs_info *fs_info = root->fs_info;
> +	struct btrfs_fs_info *fs_info;
>   	struct extent_buffer *b;
>   	int slot;
>   	int ret;
> @@ -2023,6 +2023,10 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root,
>   	int min_write_lock_level;
>   	int prev_cmp;
>
> +	if (!root)
> +		return -EINVAL;
> +
> +	fs_info = root->fs_info;
>   	might_sleep();
>
>   	lowest_level = p->lowest_level;