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

[Colin Ian King]

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@xxxxxxxxxxxxx>
>>
>> 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@xxxxxxxxxxxxx>
>> ---
>>
>> V2: move the btrfs_free_path to the out_free_ulist label as suggested by
>> ÂÂÂÂ David Sterba as the correct fix.
>>
>> ---
>> Â fs/btrfs/extent_io.c | 2 +-
>> Â 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,
>> ÂÂÂÂÂÂÂÂÂ ret = emit_last_fiemap_cache(fieinfo, &cache);
>> ÂÂÂÂÂ free_extent_map(em);
>> Â out:
>> -ÂÂÂ btrfs_free_path(path);
>> ÂÂÂÂÂ unlock_extent_cached(&BTRFS_I(inode)->io_tree, start, start +
>> len - 1,
>> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ &cached_state);
>> Â Â out_free_ulist:
>> +ÂÂÂ btrfs_free_path(path);
>> ÂÂÂÂÂ ulist_free(roots);
>> ÂÂÂÂÂ ulist_free(tmp_ulist);
>> ÂÂÂÂÂ 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,
> ÂÂÂÂÂÂÂ ret = btrfs_lookup_file_extent(NULL, root, path,
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ btrfs_ino(BTRFS_I(inode)), -1, 0);
> ÂÂÂÂÂÂÂ if (ret < 0) {
> -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ btrfs_free_path(path);
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ goto out_free_ulist;
> ÂÂÂÂÂÂÂ } else {
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ WARN_ON(!ret);
> 
>