From 28f300d23674fa01ae747c66ce861d4ee6aebe8c Mon Sep 17 00:00:00 2001 From: Pavel Emelyanov Date: Tue, 18 Sep 2007 22:46:45 -0700 Subject: Fix user namespace exiting OOPs It turned out, that the user namespace is released during the do_exit() in exit_task_namespaces(), but the struct user_struct is released only during the put_task_struct(), i.e. MUCH later. On debug kernels with poisoned slabs this will cause the oops in uid_hash_remove() because the head of the chain, which resides inside the struct user_namespace, will be already freed and poisoned. Since the uid hash itself is required only when someone can search it, i.e. when the namespace is alive, we can safely unhash all the user_struct-s from it during the namespace exiting. The subsequent free_uid() will complete the user_struct destruction. For example simple program #include char stack[2 * 1024 * 1024]; int f(void *foo) { return 0; } int main(void) { clone(f, stack + 1 * 1024 * 1024, 0x10000000, 0); return 0; } run on kernel with CONFIG_USER_NS turned on will oops the kernel immediately. This was spotted during OpenVZ kernel testing. Signed-off-by: Pavel Emelyanov Signed-off-by: Alexey Dobriyan Acked-by: "Serge E. Hallyn" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/user.c | 26 +++++++++++++++++++++++++- kernel/user_namespace.c | 2 +- 2 files changed, 26 insertions(+), 2 deletions(-) (limited to 'kernel') diff --git a/kernel/user.c b/kernel/user.c index add57c7e..9ca2848 100644 --- a/kernel/user.c +++ b/kernel/user.c @@ -62,7 +62,7 @@ static inline void uid_hash_insert(struct user_struct *up, struct hlist_head *ha static inline void uid_hash_remove(struct user_struct *up) { - hlist_del(&up->uidhash_node); + hlist_del_init(&up->uidhash_node); } static inline struct user_struct *uid_hash_find(uid_t uid, struct hlist_head *hashent) @@ -199,6 +199,30 @@ void switch_uid(struct user_struct *new_user) suid_keys(current); } +void release_uids(struct user_namespace *ns) +{ + int i; + unsigned long flags; + struct hlist_head *head; + struct hlist_node *nd; + + spin_lock_irqsave(&uidhash_lock, flags); + /* + * collapse the chains so that the user_struct-s will + * be still alive, but not in hashes. subsequent free_uid() + * will free them. + */ + for (i = 0; i < UIDHASH_SZ; i++) { + head = ns->uidhash_table + i; + while (!hlist_empty(head)) { + nd = head->first; + hlist_del_init(nd); + } + } + spin_unlock_irqrestore(&uidhash_lock, flags); + + free_uid(ns->root_user); +} static int __init uid_cache_init(void) { diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c index e7ba1bf..7af90fc 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -81,7 +81,7 @@ void free_user_ns(struct kref *kref) struct user_namespace *ns; ns = container_of(kref, struct user_namespace, kref); - free_uid(ns->root_user); + release_uids(ns); kfree(ns); } -- cgit v1.1