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From:   Stas Sergeev <stsp2@yandex.ru>
Cc:     Stas Sergeev <stsp2@yandex.ru>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Kees Cook <keescook@chromium.org>,
        Jens Axboe <axboe@kernel.dk>,
        Peter Zijlstra <peterz@infradead.org>,
        Marco Elver <elver@google.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Alexey Gladkov <legion@kernel.org>,
        Andrew Lutomirski <luto@mit.edu>, linux-kernel@vger.kernel.org
Subject: [PATCH 1/2] sigaltstack: ignore flags if SS_DISABLE is set
Date:   Wed, 26 Jan 2022 22:14:40 +0300
Message-Id: <20220126191441.3380389-2-stsp2@yandex.ru>
In-Reply-To: <20220126191441.3380389-1-stsp2@yandex.ru>
References: <20220126191441.3380389-1-stsp2@yandex.ru>
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ss_flags combo of SS_AUTODISARM|SS_DISABLE can be used to check
the support of SS_AUTODISARM. We need to remove the like flags and
only keep SS_DISABLE because many libraries (eg asan runtime)
check if SAS is disabled by just checking "ss_flags == SS_DISABLE".

Also man page mandates that only 1 flag can be returned, so
returning SS_AUTODISARM|SS_DISABLE should be disallowed.

Signed-off-by: Stas Sergeev <stsp2@yandex.ru>
CC: "Eric W. Biederman" <ebiederm@xmission.com>
CC: Kees Cook <keescook@chromium.org>
CC: Jens Axboe <axboe@kernel.dk>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Marco Elver <elver@google.com>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Alexey Gladkov <legion@kernel.org>
CC: Andrew Lutomirski <luto@mit.edu>
CC: linux-kernel@vger.kernel.org
---
 kernel/signal.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/signal.c b/kernel/signal.c
index 38602738866e..40634a500317 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -4209,6 +4209,7 @@ do_sigaltstack (const stack_t *ss, stack_t *oss, unsigned long sp,
 		if (ss_mode == SS_DISABLE) {
 			ss_size = 0;
 			ss_sp = NULL;
+			ss_flags = SS_DISABLE;
 		} else {
 			if (unlikely(ss_size < min_ss_size))
 				ret = -ENOMEM;
-- 
2.34.1