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

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Date:   Fri, 5 Jul 2019 09:30:29 +0800
From:   Anand Jain <anand.jain@...cle.com>
To:     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
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 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.

$ 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);