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

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Date:   Thu, 4 Jul 2019 19:20:07 +0200
From:   David Sterba <dsterba@...e.cz>
To:     Colin Ian King <colin.king@...onical.com>
Cc:     dsterba@...e.cz, 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 Thu, Jul 04, 2019 at 05:47:50PM +0100, Colin Ian King wrote:
> >>  	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.
> 
> Oh, yes. Even static analysis missed that too!
> 
> > Bummer that the leaks escaped sight of original patch author (me), 2
> > reviewers and now 1 fix reviewer.
> > 
> Given that you can see more issues, I'll leave the fix in your capable
> hands.

This

--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -4764,11 +4764,11 @@ 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;
---

should fix it.