linux-kernel - [PATCH for 5.5 1/3] rseq: Fix: Reject unknown flags on rseq unregister

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Message-Id: <20191211161713.4490-2-mathieu.desnoyers@efficios.com>
Date:   Wed, 11 Dec 2019 11:17:11 -0500
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        "Paul E . McKenney" <paulmck@...ux.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        "H . Peter Anvin" <hpa@...or.com>, Paul Turner <pjt@...gle.com>,
        linux-api@...r.kernel.org, stable@...r.kernel.org,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: [PATCH for 5.5 1/3] rseq: Fix: Reject unknown flags on rseq unregister

It is preferrable to reject unknown flags within rseq unregistration
rather than to ignore them. It is an oversight caused by the fact that
the check for unknown flags is after the rseq unregister flag check.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: "Paul E. McKenney" <paulmck@...ux.ibm.com>
Cc: Boqun Feng <boqun.feng@...il.com>
Cc: "H . Peter Anvin" <hpa@...or.com>
Cc: Paul Turner <pjt@...gle.com>
Cc: linux-api@...r.kernel.org
Cc: <stable@...r.kernel.org>	# v4.18+
---
 kernel/rseq.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/rseq.c b/kernel/rseq.c
index 27c48eb7de40..a4f86a9d6937 100644
--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -310,6 +310,8 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len,
 	int ret;
 
 	if (flags & RSEQ_FLAG_UNREGISTER) {
+		if (flags & ~RSEQ_FLAG_UNREGISTER)
+			return -EINVAL;
 		/* Unregister rseq for current thread. */
 		if (current->rseq != rseq || !current->rseq)
 			return -EINVAL;
-- 
2.17.1