[PATCH 5/7] audit: allow unsetting the loginuid (with priv)

If a task has CAP_AUDIT_CONTROL allow that task to unset their loginuid. This would allow a child of that task to set their loginuid without CAP_AUDIT_CONTROL. Thus when launching a new login daemon, a priviledged helper would be able to unset the loginuid and then the daemon, which may be malicious user facing, do not need priv to function correctly. Signed-off-by: Eric Paris <eparis(a)redhat.com&gt; --- fs/proc/base.c | 14 ++++++++++---- kernel/auditsc.c | 4 +++- 2 files changed, 13 insertions(+), 5 deletions(-) diff --git a/fs/proc/base.c b/fs/proc/base.c index 69078c7..33d0d0b 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -1119,10 +1119,16 @@ static ssize_t proc_loginuid_write(struct file * file, const char __user * buf, goto out_free_page; } - kloginuid = make_kuid(file->f_cred->user_ns, loginuid); - if (!uid_valid(kloginuid)) { - length = -EINVAL; - goto out_free_page; + + /* is userspace tring to explicitly UNSET the loginuid? */ + if (loginuid == AUDIT_UID_UNSET) { + kloginuid = INVALID_UID; + } else { + kloginuid = make_kuid(file->f_cred->user_ns, loginuid); + if (!uid_valid(kloginuid)) { + length = -EINVAL; + goto out_free_page; + } } length = audit_set_loginuid(kloginuid); diff --git a/kernel/auditsc.c b/kernel/auditsc.c index bbc5a4f..eea28c1 100644 --- a/kernel/auditsc.c +++ b/kernel/auditsc.c @@ -2017,7 +2017,9 @@ int audit_set_loginuid(kuid_t loginuid) if (rc) goto out; - sessionid = atomic_inc_return(&session_id); + /* are we setting or clearing? */ + if (uid_valid(loginuid)) + sessionid = atomic_inc_return(&session_id); task->sessionid = sessionid; task->loginuid = loginuid; -- 1.8.2.1