linux-kernel - Re: [PATCH] btrfs: fix dereference on inode->i

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Date:   Fri, 16 Dec 2016 10:03:33 -0500
From:   Jeff Mahoney <jeffm@...e.com>
To:     Colin King <colin.king@...onical.com>, Chris Mason <clm@...com>,
        Josef Bacik <jbacik@...com>, David Sterba <dsterba@...e.com>,
        linux-btrfs@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] btrfs: fix dereference on inode->i_sb before inode null
 check

On 12/16/16 7:20 AM, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> inode is being deferenced and then inode is checked to see if it
> is null, implying we potentially could have a null pointer deference
> on inode.
> 
> Found with static analysis by CoverityScan, CID 1389472
> 
> Fix this by dereferencing inode only after the inode null check.
> 
> Fixes: 0b246afa62b0cf5 ("btrfs: root->fs_info cleanup, add fs_info convenience variables")

Hi Colin -

Thanks for the review.  The right fix here is to eliminate the tests for
inode == NULL entirely.  This is a callback for exportfs, which will
itself crash if dentry->d_inode or parent->d_inode is NULL.  Removing
the tests would be consistent with other file systems.

-Jeff

> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
>  fs/btrfs/export.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/export.c b/fs/btrfs/export.c
> index 340d907..b746d2b 100644
> --- a/fs/btrfs/export.c
> +++ b/fs/btrfs/export.c
> @@ -223,7 +223,7 @@ static int btrfs_get_name(struct dentry *parent, char *name,
>  {
>  	struct inode *inode = d_inode(child);
>  	struct inode *dir = d_inode(parent);
> -	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
> +	struct btrfs_fs_info *fs_info;
>  	struct btrfs_path *path;
>  	struct btrfs_root *root = BTRFS_I(dir)->root;
>  	struct btrfs_inode_ref *iref;
> @@ -241,6 +241,7 @@ static int btrfs_get_name(struct dentry *parent, char *name,
>  	if (!S_ISDIR(dir->i_mode))
>  		return -EINVAL;
>  
> +	fs_info = btrfs_sb(inode->i_sb);
>  	ino = btrfs_ino(inode);
>  
>  	path = btrfs_alloc_path();
> 


-- 
Jeff Mahoney
SUSE Labs



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