From a8b0026847b8c43445c921ad2c85521c92eb175f Mon Sep 17 00:00:00 2001 From: Al Viro Date: Mon, 20 Nov 2023 20:02:11 -0500 Subject: rename(): avoid a deadlock in the case of parents having no common ancestor ... and fix the directory locking documentation and proof of correctness. Holding ->s_vfs_rename_mutex *almost* prevents ->d_parent changes; the case where we really don't want it is splicing the root of disconnected tree to somewhere. In other words, ->s_vfs_rename_mutex is sufficient to stabilize "X is an ancestor of Y" only if X and Y are already in the same tree. Otherwise it can go from false to true, and one can construct a deadlock on that. Make lock_two_directories() report an error in such case and update the callers of lock_rename()/lock_rename_child() to handle such errors. And yes, such conditions are not impossible to create ;-/ Reviewed-by: Jan Kara Signed-off-by: Al Viro --- fs/overlayfs/util.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) (limited to 'fs/overlayfs/util.c') diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c index 50a201e9cd39..7b667345e673 100644 --- a/fs/overlayfs/util.c +++ b/fs/overlayfs/util.c @@ -1198,12 +1198,17 @@ void ovl_nlink_end(struct dentry *dentry) int ovl_lock_rename_workdir(struct dentry *workdir, struct dentry *upperdir) { + struct dentry *trap; + /* Workdir should not be the same as upperdir */ if (workdir == upperdir) goto err; /* Workdir should not be subdir of upperdir and vice versa */ - if (lock_rename(workdir, upperdir) != NULL) + trap = lock_rename(workdir, upperdir); + if (IS_ERR(trap)) + goto err; + if (trap) goto err_unlock; return 0; -- cgit v1.2.3