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proc: prevent changes to overridden credentials

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commit 35a196bef4 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>
This commit is contained in:
Paul Moore 2019-04-19 14:55:12 -04:00 committed by Greg Kroah-Hartman
parent bbd559ad3c
commit 7928396df9
1 changed files with 5 additions and 0 deletions
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5
fs/proc/base.c
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@ -2542,6 +2542,11 @@ 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)