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authorEric W. Biederman <ebiederm@xmission.com>2012-07-26 16:05:21 +0400
committerEric W. Biederman <ebiederm@xmission.com>2012-11-20 16:17:44 +0400
commit4c44aaafa8108f584831850ab48a975e971db2de (patch)
treec86f225e8256d28271acf3ea8926e70358f3e5c1
parentbcf58e725ddc45d31addbc6627d4f0edccc824c1 (diff)
downloadlinux-4c44aaafa8108f584831850ab48a975e971db2de.tar.xz
userns: Kill task_user_ns
The task_user_ns function hides the fact that it is getting the user namespace from struct cred on the task. struct cred may go away as soon as the rcu lock is released. This leads to a race where we can dereference a stale user namespace pointer. To make it obvious a struct cred is involved kill task_user_ns. To kill the race modify the users of task_user_ns to only reference the user namespace while the rcu lock is held. Cc: Kees Cook <keescook@chromium.org> Cc: James Morris <james.l.morris@oracle.com> Acked-by: Kees Cook <keescook@chromium.org> Acked-by: Serge Hallyn <serge.hallyn@canonical.com> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
-rw-r--r--include/linux/cred.h2
-rw-r--r--kernel/ptrace.c10
-rw-r--r--kernel/sched/core.c10
-rw-r--r--security/yama/yama_lsm.c12
4 files changed, 25 insertions, 9 deletions
diff --git a/include/linux/cred.h b/include/linux/cred.h
index ebbed2ce6637..856d2622d832 100644
--- a/include/linux/cred.h
+++ b/include/linux/cred.h
@@ -357,10 +357,8 @@ static inline void put_cred(const struct cred *_cred)
extern struct user_namespace init_user_ns;
#ifdef CONFIG_USER_NS
#define current_user_ns() (current_cred_xxx(user_ns))
-#define task_user_ns(task) (task_cred_xxx((task), user_ns))
#else
#define current_user_ns() (&init_user_ns)
-#define task_user_ns(task) (&init_user_ns)
#endif
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 1f5e55dda955..7b09b88862cc 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -215,8 +215,12 @@ ok:
smp_rmb();
if (task->mm)
dumpable = get_dumpable(task->mm);
- if (!dumpable && !ptrace_has_cap(task_user_ns(task), mode))
+ rcu_read_lock();
+ if (!dumpable && !ptrace_has_cap(__task_cred(task)->user_ns, mode)) {
+ rcu_read_unlock();
return -EPERM;
+ }
+ rcu_read_unlock();
return security_ptrace_access_check(task, mode);
}
@@ -280,8 +284,10 @@ static int ptrace_attach(struct task_struct *task, long request,
if (seize)
flags |= PT_SEIZED;
- if (ns_capable(task_user_ns(task), CAP_SYS_PTRACE))
+ rcu_read_lock();
+ if (ns_capable(__task_cred(task)->user_ns, CAP_SYS_PTRACE))
flags |= PT_PTRACE_CAP;
+ rcu_read_unlock();
task->ptrace = flags;
__ptrace_link(task, current);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 2d8927fda712..2f5eb1838b3e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4029,8 +4029,14 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
goto out_free_cpus_allowed;
}
retval = -EPERM;
- if (!check_same_owner(p) && !ns_capable(task_user_ns(p), CAP_SYS_NICE))
- goto out_unlock;
+ if (!check_same_owner(p)) {
+ rcu_read_lock();
+ if (!ns_capable(__task_cred(p)->user_ns, CAP_SYS_NICE)) {
+ rcu_read_unlock();
+ goto out_unlock;
+ }
+ rcu_read_unlock();
+ }
retval = security_task_setscheduler(p);
if (retval)
diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c
index b4c29848b49d..0e72239aeb05 100644
--- a/security/yama/yama_lsm.c
+++ b/security/yama/yama_lsm.c
@@ -262,14 +262,18 @@ int yama_ptrace_access_check(struct task_struct *child,
/* No additional restrictions. */
break;
case YAMA_SCOPE_RELATIONAL:
+ rcu_read_lock();
if (!task_is_descendant(current, child) &&
!ptracer_exception_found(current, child) &&
- !ns_capable(task_user_ns(child), CAP_SYS_PTRACE))
+ !ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE))
rc = -EPERM;
+ rcu_read_unlock();
break;
case YAMA_SCOPE_CAPABILITY:
- if (!ns_capable(task_user_ns(child), CAP_SYS_PTRACE))
+ rcu_read_lock();
+ if (!ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE))
rc = -EPERM;
+ rcu_read_unlock();
break;
case YAMA_SCOPE_NO_ATTACH:
default:
@@ -307,8 +311,10 @@ int yama_ptrace_traceme(struct task_struct *parent)
/* Only disallow PTRACE_TRACEME on more aggressive settings. */
switch (ptrace_scope) {
case YAMA_SCOPE_CAPABILITY:
- if (!ns_capable(task_user_ns(parent), CAP_SYS_PTRACE))
+ rcu_read_lock();
+ if (!ns_capable(__task_cred(parent)->user_ns, CAP_SYS_PTRACE))
rc = -EPERM;
+ rcu_read_unlock();
break;
case YAMA_SCOPE_NO_ATTACH:
rc = -EPERM;