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

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Date:   Thu, 4 Jul 2019 18:37:21 +0200
From:   David Sterba <dsterba@...e.cz>
To:     Colin King <colin.king@...onical.com>
Cc:     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 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.