From 35a196bef449b5824033865b963ed9a43fb8c730 Mon Sep 17 00:00:00 2001
From: Paul Moore <paul@paul-moore.com>
Date: Fri, 19 Apr 2019 14:55:12 -0400
Subject: [PATCH] proc: prevent changes to overridden credentials
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>
---
fs/proc/base.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/fs/proc/base.c b/fs/proc/base.c
index ddef482f13340..87ba007b86dbb 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2539,6 +2539,11 @@ static ssize_t proc_pid_attr_write(struct file * file, const char __user * buf,
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)
--
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