[PATCH 5.1 036/122] proc: prevent changes to overridden credentials

Greg Kroah-Hartman
2019-05-23T19:27:12Z

From: Paul Moore <paul@paul-moore.com>

commit 35a196bef449b5824033865b963ed9a43fb8c730 upstream.

Prevent userspace from changing the the /proc/PID/attr values if the
task's credentials are currently overriden. This not only makes sense
conceptually, it also prevents some really bizarre error cases caused
when trying to commit credentials to a task with overridden
credentials.

Cc: <stable@vger.kernel.org>
Reported-by: "chengjian (D)" <cj.chengjian@huawei.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Acked-by: John Johansen <john.johansen@canonical.com>
Acked-by: James Morris <james.morris@microsoft.com>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/proc/base.c | 5 +++++
1 file changed, 5 insertions(+)

--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2540,6 +2540,11 @@ static ssize_t proc_pid_attr_write(struc
rcu_read_unlock();
return -EACCES;
}
+ /* Prevent changes to overridden credentials. */
+ if (current_cred() != current_real_cred()) {
+ rcu_read_unlock();
+ return -EBUSY;
+ }
rcu_read_unlock();

if (count > PAGE_SIZE)