[PATCH 6/8] btrfs: clear BTRFS_ROOT_DEAD_RELOC_TREE before dropping the reloc root

Josef Bacik
2020-03-13T15:45:47Z

Qu put this in place in order to avoid a use after free in
init_reloc_root. However a previous patch in this series makes the use
after free impossible because at this point we no longer have a
reloc_control set on the fs_info.

So move this to be coupled with clearing the root->reloc_root so we're
consistent with all other operations of the reloc root.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
fs/btrfs/relocation.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 9c8a4a4b2bde..5bbed0ea26e1 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -2291,18 +2291,19 @@ static int clean_dirty_subvols(struct reloc_control *rc)

list_del_init(&root->reloc_dirty_list);
root->reloc_root = NULL;
- if (reloc_root) {
-
- ret2 = btrfs_drop_snapshot(reloc_root, NULL, 0, 1);
- if (ret2 < 0 && !ret)
- ret = ret2;
- }
/*
* Need barrier to ensure clear_bit() only happens after
* root->reloc_root = NULL. Pairs with have_reloc_root.
*/
smp_wmb();
clear_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state);
+
+ if (reloc_root) {
+
+ ret2 = btrfs_drop_snapshot(reloc_root, NULL, 0, 1);
+ if (ret2 < 0 && !ret)
+ ret = ret2;
+ }
btrfs_put_root(root);
} else {
/* Orphan reloc tree, just clean it up */
--
2.24.1