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

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Message-ID: <2d2ef70f-c07d-8062-924d-e7d88b8d98fa@canonical.com>
Date:   Fri, 16 Dec 2016 15:24:41 +0000
From:   Colin Ian King <colin.king@...onical.com>
To:     Jeff Mahoney <jeffm@...e.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 16/12/16 15:03, Jeff Mahoney wrote:
> 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.

Ah, thanks for pointing that out. New patch on it's way soon.

Colin

> 
> -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();
>>
> 
> 




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