linux-kernel - Re: [PATCH][next] btrfs: fix memory leak of path on error return path

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Date:   Fri, 5 Jul 2019 09:28:57 +0800
From:   Anand Jain <anand.jain@...cle.com>
To:     dsterba@...e.cz, Colin King <colin.king@...onical.com>,
        Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] btrfs: fix memory leak of path on error return path

On 5/7/19 12:37 AM, David Sterba wrote:
> On Tue, Jul 02, 2019 at 03:10:28PM +0100, Colin King wrote:
>> From: Colin Ian King <colin.king@...onical.com>
>>
>> Currently if the allocation of roots or tmp_ulist fails the error handling
>> does not free up the allocation of path causing a memory leak. Fix this by
>> freeing path with a call to btrfs_free_path before taking the error return
>> path.
>>
>> Addresses-Coverity: ("Resource leak")
> 
> Does this have an id, that coverity uses?
> 
>> Fixes: 5911c8fe05c5 ("btrfs: fiemap: preallocate ulists for btrfs_check_shared")
>> Signed-off-by: Colin Ian King <colin.king@...onical.com>
>> ---
>>   fs/btrfs/extent_io.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
>> index 1eb671c16ff1..d7f37a33d597 100644
>> --- a/fs/btrfs/extent_io.c
>> +++ b/fs/btrfs/extent_io.c
>> @@ -4600,6 +4600,7 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
>>   	tmp_ulist = ulist_alloc(GFP_KERNEL);
>>   	if (!roots || !tmp_ulist) {
>>   		ret = -ENOMEM;
>> +		btrfs_free_path(path);
> 
> This fixes only one leak, therere are more that I spotted while
> reviewing this patch. The gotos from the while-loop jump to
> out_free_list but that leave the path behind.
> 
> That's why the exit block is a better place for the cleanups. This
> requires proper nesting of the cleanup calls, that's slightly
> inconvenient in this case. The free_path is before call to
> unlock_extent_cached so when the ordre is switched and free_path moved
> to out_free_ulist, then all the leaks are addressed in one go.
> 
> Bummer that the leaks escaped sight of original patch author (me), 2
> reviewers and now 1 fix reviewer.
> 

There is no goto out_free_ulist inside the while loop; where do you see
that? I did git pull again and checked.

4664         while (!end) {
::
4726                                 goto out_free;
::
4748                         goto out;
::
4759                         goto out_free;
::
4761         }