linux-kernel - Re: [PATCH] btrfs: fix a NULL pointer dereference

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Message-ID: <b0b494f4-8686-8e50-faca-625d6f89bbe3@suse.com>
Date:   Thu, 14 Mar 2019 09:54:07 +0200
From:   Nikolay Borisov <nborisov@...e.com>
To:     Kangjie Lu <kjlu@....edu>
Cc:     pakki001@....edu, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] btrfs: fix a NULL pointer dereference



On 14.03.19 г. 9:50 ч., Kangjie Lu wrote:
> btrfs_lookup_block_group may fail and return NULL. The fix goes
> to out when it fails to avoid NULL pointer dereference.

Actually no, in this case btrfs_lookup_block_group must never fail
because if we have an allocated eb then it must have been allocated from
a bg.

> 
> Signed-off-by: Kangjie Lu <kjlu@....edu>
> ---
>  fs/btrfs/extent-tree.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 994f0cc41799..b1e7985bcb9d 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -7303,6 +7303,8 @@ void btrfs_free_tree_block(struct btrfs_trans_handle *trans,
>  
>  		pin = 0;
>  		cache = btrfs_lookup_block_group(fs_info, buf->start);
> +		if (!cache)
> +			goto out;
>  
>  		if (btrfs_header_flag(buf, BTRFS_HEADER_FLAG_WRITTEN)) {
>  			pin_down_extent(fs_info, cache, buf->start,
>