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SubjectRe: [PATCH][next][V2] btrfs: fix memory leak of path on error return path
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On 5/7/19 7:03 AM, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.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@canonical.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);

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