From 5170836679185357dc1b7660bad13287b39e1e33 Mon Sep 17 00:00:00 2001 From: David Howells Date: Fri, 27 Feb 2009 14:03:03 -0800 Subject: [PATCH] Fix recursive lock in free_uid()/free_user_ns() free_uid() and free_user_ns() are corecursive when CONFIG_USER_SCHED=n, but free_user_ns() is called from free_uid() by way of uid_hash_remove(), which requires uidhash_lock to be held. free_user_ns() then calls free_uid() to complete the destruction. Fix this by deferring the destruction of the user_namespace. Signed-off-by: David Howells Acked-by: Serge Hallyn Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/user_namespace.h | 1 + kernel/user_namespace.c | 21 +++++++++++++++++---- 2 files changed, 18 insertions(+), 4 deletions(-) diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h index 315bcd375224..cc4f45361dbb 100644 --- a/include/linux/user_namespace.h +++ b/include/linux/user_namespace.h @@ -13,6 +13,7 @@ struct user_namespace { struct kref kref; struct hlist_head uidhash_table[UIDHASH_SZ]; struct user_struct *creator; + struct work_struct destroyer; }; extern struct user_namespace init_user_ns; diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c index 79084311ee57..076c7c8215b0 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -60,12 +60,25 @@ int create_user_ns(struct cred *new) return 0; } -void free_user_ns(struct kref *kref) +/* + * Deferred destructor for a user namespace. This is required because + * free_user_ns() may be called with uidhash_lock held, but we need to call + * back to free_uid() which will want to take the lock again. + */ +static void free_user_ns_work(struct work_struct *work) { - struct user_namespace *ns; - - ns = container_of(kref, struct user_namespace, kref); + struct user_namespace *ns = + container_of(work, struct user_namespace, destroyer); free_uid(ns->creator); kfree(ns); } + +void free_user_ns(struct kref *kref) +{ + struct user_namespace *ns = + container_of(kref, struct user_namespace, kref); + + INIT_WORK(&ns->destroyer, free_user_ns_work); + schedule_work(&ns->destroyer); +} EXPORT_SYMBOL(free_user_ns); -- 2.20.1