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Fix recursive lock in free_uid()/free_user_ns()

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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 <dhowells@redhat.com>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
David Howells 2009-02-27 14:03:03 -08:00 committed by Linus Torvalds
parent 8ca2f156b0
commit 5170836679
2 changed files with 18 additions and 4 deletions
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1
include/linux/user_namespace.h
View File

@ -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;

21
kernel/user_namespace.c
View File

@ -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);