Re: [PATCH] fuse: Fix a potential double free in virtio_fs_get_tree
From: Vivek Goyal <vgoyal@redhat.com>
Date: 2021-03-23 17:10:52
Also in:
linux-fsdevel, lkml
On Mon, Mar 22, 2021 at 10:18:31PM -0700, Lv Yunlong wrote:
In virtio_fs_get_tree, fm is allocated by kzalloc() and assigned to fsc->s_fs_info by fsc->s_fs_info=fm statement. If the kzalloc() failed, it will goto err directly, so that fsc->s_fs_info must be non-NULL and fm will be freed.
sget_fc() will either consume fsc->s_fs_info in case a new super
block is allocated and set fsc->s_fs_info. In that case we don't
free fc or fm.
Or, sget_fc() will return with fsc->s_fs_info set in case we already
found a super block. In that case we need to free fc and fm.
In case of error from sget_fc(), fc/fm need to be freed first and
then error needs to be returned to caller.
if (IS_ERR(sb))
return PTR_ERR(sb);
If we allocated a new super block in sget_fc(), then next step is
to initialize it.
if (!sb->s_root) {
err = virtio_fs_fill_super(sb, fsc);
}
If we run into errors here, then fc/fm need to be freed.
So current code looks fine to me.
Vivek
quoted hunk
But later fm is freed again when virtio_fs_fill_super() fialed. I think the statement if (fsc->s_fs_info) {kfree(fm);} is misplaced. My patch puts this statement in the correct palce to avoid double free. Signed-off-by: Lv Yunlong <redacted> --- fs/fuse/virtio_fs.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-)diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c index 8868ac31a3c0..727cf436828f 100644 --- a/fs/fuse/virtio_fs.c +++ b/fs/fuse/virtio_fs.c@@ -1437,10 +1437,7 @@ static int virtio_fs_get_tree(struct fs_context *fsc) fsc->s_fs_info = fm; sb = sget_fc(fsc, virtio_fs_test_super, set_anon_super_fc); - if (fsc->s_fs_info) { - fuse_conn_put(fc); - kfree(fm); - } + if (IS_ERR(sb)) return PTR_ERR(sb);@@ -1457,6 +1454,11 @@ static int virtio_fs_get_tree(struct fs_context *fsc) sb->s_flags |= SB_ACTIVE; } + if (fsc->s_fs_info) { + fuse_conn_put(fc); + kfree(fm); + } + WARN_ON(fsc->root); fsc->root = dget(sb->s_root); return 0;-- 2.25.1
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