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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Sargun Dhillon <sargun@sargun.me>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Aleksa Sarai <cyphar@cyphar.com>,
        Tycho Andersen <tycho@tycho.ws>,
        Kees Cook <keescook@chromium.org>
Subject: [PATCH 5.4 094/191] seccomp: Check that seccomp_notif is zeroed out by the user
Date:   Tue,  7 Jan 2020 21:53:34 +0100
Message-Id: <20200107205338.024294053@linuxfoundation.org>
In-Reply-To: <20200107205332.984228665@linuxfoundation.org>
References: <20200107205332.984228665@linuxfoundation.org>
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From: Sargun Dhillon <sargun@sargun.me>

commit 2882d53c9c6f3b8311d225062522f03772cf0179 upstream.

This patch is a small change in enforcement of the uapi for
SECCOMP_IOCTL_NOTIF_RECV ioctl. Specifically, the datastructure which
is passed (seccomp_notif) must be zeroed out. Previously any of its
members could be set to nonsense values, and we would ignore it.

This ensures all fields are set to their zero value.

Signed-off-by: Sargun Dhillon <sargun@sargun.me>
Reviewed-by: Christian Brauner <christian.brauner@ubuntu.com>
Reviewed-by: Aleksa Sarai <cyphar@cyphar.com>
Acked-by: Tycho Andersen <tycho@tycho.ws>
Link: https://lore.kernel.org/r/20191229062451.9467-2-sargun@sargun.me
Fixes: 6a21cc50f0c7 ("seccomp: add a return code to trap to userspace")
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 kernel/seccomp.c |    7 +++++++
 1 file changed, 7 insertions(+)

--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -1015,6 +1015,13 @@ static long seccomp_notify_recv(struct s
 	struct seccomp_notif unotif;
 	ssize_t ret;
 
+	/* Verify that we're not given garbage to keep struct extensible. */
+	ret = check_zeroed_user(buf, sizeof(unotif));
+	if (ret < 0)
+		return ret;
+	if (!ret)
+		return -EINVAL;
+
 	memset(&unotif, 0, sizeof(unotif));
 
 	ret = down_interruptible(&filter->notif->request);