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From:   Ricardo Ribalda <ribalda@chromium.org>
Date:   Wed, 21 Dec 2022 13:50:02 +0100
Subject: [PATCH v4 2/3] kexec: Factor out kexec_load_permitted
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Message-Id: <20221114-disable-kexec-reset-v4-2-ab809c8d988c@chromium.org>
References: <20221114-disable-kexec-reset-v4-0-ab809c8d988c@chromium.org>
In-Reply-To: <20221114-disable-kexec-reset-v4-0-ab809c8d988c@chromium.org>
To:     Jonathan Corbet <corbet@lwn.net>, Philipp Rudo <prudo@redhat.com>,
        Eric Biederman <ebiederm@xmission.com>,
        "Guilherme G. Piccoli" <gpiccoli@igalia.com>
Cc:     kexec@lists.infradead.org, Ricardo Ribalda <ribalda@chromium.org>,
        Ross Zwisler <zwisler@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        "Joel Fernandes (Google)" <joel@joelfernandes.org>,
        Sergey Senozhatsky <senozhatsky@chromium.org>,
        linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org
Precedence: bulk

Both syscalls (kexec and kexec_file) do the same check, lets factor it
out.

Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
---
 include/linux/kexec.h |  3 ++-
 kernel/kexec.c        |  2 +-
 kernel/kexec_core.c   | 11 ++++++++++-
 kernel/kexec_file.c   |  2 +-
 4 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 41a686996aaa..182e0c11b87b 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -406,7 +406,8 @@ extern int kimage_crash_copy_vmcoreinfo(struct kimage *image);
 
 extern struct kimage *kexec_image;
 extern struct kimage *kexec_crash_image;
-extern int kexec_load_disabled;
+
+bool kexec_load_permitted(void);
 
 #ifndef kexec_flush_icache_page
 #define kexec_flush_icache_page(page)
diff --git a/kernel/kexec.c b/kernel/kexec.c
index cb8e6e6f983c..ce1bca874a8d 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -193,7 +193,7 @@ static inline int kexec_load_check(unsigned long nr_segments,
 	int result;
 
 	/* We only trust the superuser with rebooting the system. */
-	if (!capable(CAP_SYS_BOOT) || kexec_load_disabled)
+	if (!kexec_load_permitted())
 		return -EPERM;
 
 	/* Permit LSMs and IMA to fail the kexec */
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index ca2743f9c634..a1efc70f4158 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -928,7 +928,7 @@ int kimage_load_segment(struct kimage *image,
 
 struct kimage *kexec_image;
 struct kimage *kexec_crash_image;
-int kexec_load_disabled;
+static int kexec_load_disabled;
 #ifdef CONFIG_SYSCTL
 static struct ctl_table kexec_core_sysctls[] = {
 	{
@@ -952,6 +952,15 @@ static int __init kexec_core_sysctl_init(void)
 late_initcall(kexec_core_sysctl_init);
 #endif
 
+bool kexec_load_permitted(void)
+{
+	/*
+	 * Only the superuser can use the kexec syscall and if it has not
+	 * been disabled.
+	 */
+	return capable(CAP_SYS_BOOT) && !kexec_load_disabled;
+}
+
 /*
  * No panic_cpu check version of crash_kexec().  This function is called
  * only when panic_cpu holds the current CPU number; this is the only CPU
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 45637511e0de..29efa43ea951 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -330,7 +330,7 @@ SYSCALL_DEFINE5(kexec_file_load, int, kernel_fd, int, initrd_fd,
 	struct kimage **dest_image, *image;
 
 	/* We only trust the superuser with rebooting the system. */
-	if (!capable(CAP_SYS_BOOT) || kexec_load_disabled)
+	if (!kexec_load_permitted())
 		return -EPERM;
 
 	/* Make sure we have a legal set of flags */

-- 
2.39.0.314.g84b9a713c41-goog-b4-0.11.0-dev-696ae