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authorPavel Emelyanov <xemul@openvz.org>2007-09-18 22:46:45 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-09-19 11:24:18 -0700
commit28f300d23674fa01ae747c66ce861d4ee6aebe8c (patch)
tree52ea69a57a89760d7060597690cb289d049eb4d0
parent735de2230f09741077a645a913de0a04b10208bf (diff)
downloadlinux-linaro-28f300d23674fa01ae747c66ce861d4ee6aebe8c.tar.gz
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 <sched.h> 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 <xemul@openvz.org> Signed-off-by: Alexey Dobriyan <adobriyan@openvz.org> Acked-by: "Serge E. Hallyn" <serue@us.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--include/linux/sched.h1
-rw-r--r--kernel/user.c26
-rw-r--r--kernel/user_namespace.c2
3 files changed, 27 insertions, 2 deletions
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 6239bc2c2ba..5445eaec690 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1472,6 +1472,7 @@ static inline struct user_struct *get_uid(struct user_struct *u)
}
extern void free_uid(struct user_struct *);
extern void switch_uid(struct user_struct *);
+extern void release_uids(struct user_namespace *ns);
#include <asm/current.h>
diff --git a/kernel/user.c b/kernel/user.c
index add57c7e4c0..9ca2848fc35 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 e7ba1bf8457..7af90fc4f0f 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);
}