linux-kernel - Re: [PATCH][next][V2] btrfs: fix memory leak of path on error return path

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Message-ID: <18f120a8-15f9-b0d6-97c2-2a1091f7022d@canonical.com>
Date:   Fri, 5 Jul 2019 08:14:34 +0100
From:   Colin Ian King <colin.king@...onical.com>
To:     Anand Jain <anand.jain@...cle.com>, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next][V2] btrfs: fix memory leak of path on error return
 path

On 05/07/2019 02:30, Anand Jain wrote:
> On 5/7/19 7:03 AM, 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 and
>> other similar leaks by moving the call of btrfs_free_path from label out
>> to label out_free_ulist.
>>
>> Kudos to David Sterba for spotting the issue in my original fix and
>> providing the correct way to fix the leak.
>>
>> Addresses-Coverity: ("Resource leak")
>> Fixes: 5911c8fe05c5 ("btrfs: fiemap: preallocate ulists for
>> btrfs_check_shared")
>> Signed-off-by: Colin Ian King <colin.king@...onical.com>
>> ---
>>
>> V2: move the btrfs_free_path to the out_free_ulist label as suggested by
>>      David Sterba as the correct fix.
>>
>> ---
>>   fs/btrfs/extent_io.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
>> index 1eb671c16ff1..31127f6d2971 100644
>> --- a/fs/btrfs/extent_io.c
>> +++ b/fs/btrfs/extent_io.c
>> @@ -4766,11 +4766,11 @@ int extent_fiemap(struct inode *inode, struct
>> fiemap_extent_info *fieinfo,
>>           ret = emit_last_fiemap_cache(fieinfo, &cache);
>>       free_extent_map(em);
>>   out:
>> -    btrfs_free_path(path);
>>       unlock_extent_cached(&BTRFS_I(inode)->io_tree, start, start +
>> len - 1,
>>                    &cached_state);
>>     out_free_ulist:
>> +    btrfs_free_path(path);
>>       ulist_free(roots);
>>       ulist_free(tmp_ulist);
>>       return ret;
>>
> 
> Now this causes double free.

Thanks for spotting that, I'll send a V3
> 
> $ git diff
> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> index 6b154bce5687..61ebdccca04b 100644
> --- a/fs/btrfs/extent_io.c
> +++ b/fs/btrfs/extent_io.c
> @@ -4611,7 +4611,6 @@ int extent_fiemap(struct inode *inode, struct
> fiemap_extent_info *fieinfo,
>         ret = btrfs_lookup_file_extent(NULL, root, path,
>                         btrfs_ino(BTRFS_I(inode)), -1, 0);
>         if (ret < 0) {
> -               btrfs_free_path(path);
>                 goto out_free_ulist;
>         } else {
>                 WARN_ON(!ret);
> 
>