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From: David Howells <dhowells@redhat.com>
To: linux-security-module@vger.kernel.org
Cc: gnomes@lxorguk.ukuu.org.uk, linux-efi@vger.kernel.org,
	matthew.garrett@nebula.com, gregkh@linuxfoundation.org,
	linux-kernel@vger.kernel.org, dhowells@redhat.com,
	jforbes@redhat.com
Subject: [PATCH 02/27] Add a SysRq option to lift kernel lockdown
Date: Thu, 19 Oct 2017 15:50:47 +0100
Message-ID: <150842464774.7923.7951986297563109339.stgit@warthog.procyon.org.uk> (raw)
In-Reply-To: <150842463163.7923.11081723749106843698.stgit@warthog.procyon.org.uk>

From: Kyle McMartin <kyle@redhat.com>

Make an option to provide a sysrq key that will lift the kernel lockdown,
thereby allowing the running kernel image to be accessed and modified.

On x86_64 this is triggered with SysRq+x, but this key may not be available
on all arches, so it is set by setting LOCKDOWN_LIFT_KEY in asm/setup.h.

Signed-off-by: Kyle McMartin <kyle@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: x86@kernel.org
---

 arch/x86/include/asm/setup.h |    2 ++
 drivers/input/misc/uinput.c  |    1 +
 drivers/tty/sysrq.c          |   19 +++++++++++------
 include/linux/input.h        |    5 ++++
 include/linux/sysrq.h        |    8 ++++++-
 kernel/debug/kdb/kdb_main.c  |    2 +-
 security/Kconfig             |   15 +++++++++++++
 security/lock_down.c         |   48 ++++++++++++++++++++++++++++++++++++++++++
 8 files changed, 92 insertions(+), 8 deletions(-)

diff --git a/arch/x86/include/asm/setup.h b/arch/x86/include/asm/setup.h
index a65cf544686a..863f77582c09 100644
--- a/arch/x86/include/asm/setup.h
+++ b/arch/x86/include/asm/setup.h
@@ -8,6 +8,8 @@
 #include <linux/linkage.h>
 #include <asm/page_types.h>
 
+#define LOCKDOWN_LIFT_KEY 'x'
+
 #ifdef __i386__
 
 #include <linux/pfn.h>
diff --git a/drivers/input/misc/uinput.c b/drivers/input/misc/uinput.c
index 443151de90c6..45a1f5460805 100644
--- a/drivers/input/misc/uinput.c
+++ b/drivers/input/misc/uinput.c
@@ -408,6 +408,7 @@ static int uinput_allocate_device(struct uinput_device *udev)
 	if (!udev->dev)
 		return -ENOMEM;
 
+	udev->dev->flags |= INPUTDEV_FLAGS_SYNTHETIC;
 	udev->dev->event = uinput_dev_event;
 	input_set_drvdata(udev->dev, udev);
 
diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index 3ffc1ce29023..8b766dbad6dd 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -481,6 +481,7 @@ static struct sysrq_key_op *sysrq_key_table[36] = {
 	/* x: May be registered on mips for TLB dump */
 	/* x: May be registered on ppc/powerpc for xmon */
 	/* x: May be registered on sparc64 for global PMU dump */
+	/* x: May be registered on x86_64 for disabling secure boot */
 	NULL,				/* x */
 	/* y: May be registered on sparc64 for global register dump */
 	NULL,				/* y */
@@ -524,7 +525,7 @@ static void __sysrq_put_key_op(int key, struct sysrq_key_op *op_p)
                 sysrq_key_table[i] = op_p;
 }
 
-void __handle_sysrq(int key, bool check_mask)
+void __handle_sysrq(int key, unsigned int from)
 {
 	struct sysrq_key_op *op_p;
 	int orig_log_level;
@@ -544,11 +545,15 @@ void __handle_sysrq(int key, bool check_mask)
 
         op_p = __sysrq_get_key_op(key);
         if (op_p) {
+		/* Ban synthetic events from some sysrq functionality */
+		if ((from == SYSRQ_FROM_PROC || from == SYSRQ_FROM_SYNTHETIC) &&
+		    op_p->enable_mask & SYSRQ_DISABLE_USERSPACE)
+			printk("This sysrq operation is disabled from userspace.\n");
 		/*
 		 * Should we check for enabled operations (/proc/sysrq-trigger
 		 * should not) and is the invoked operation enabled?
 		 */
-		if (!check_mask || sysrq_on_mask(op_p->enable_mask)) {
+		if (from == SYSRQ_FROM_KERNEL || sysrq_on_mask(op_p->enable_mask)) {
 			pr_cont("%s\n", op_p->action_msg);
 			console_loglevel = orig_log_level;
 			op_p->handler(key);
@@ -580,7 +585,7 @@ void __handle_sysrq(int key, bool check_mask)
 void handle_sysrq(int key)
 {
 	if (sysrq_on())
-		__handle_sysrq(key, true);
+		__handle_sysrq(key, SYSRQ_FROM_KERNEL);
 }
 EXPORT_SYMBOL(handle_sysrq);
 
@@ -661,7 +666,7 @@ static void sysrq_do_reset(unsigned long _state)
 static void sysrq_handle_reset_request(struct sysrq_state *state)
 {
 	if (state->reset_requested)
-		__handle_sysrq(sysrq_xlate[KEY_B], false);
+		__handle_sysrq(sysrq_xlate[KEY_B], SYSRQ_FROM_KERNEL);
 
 	if (sysrq_reset_downtime_ms)
 		mod_timer(&state->keyreset_timer,
@@ -812,8 +817,10 @@ static bool sysrq_handle_keypress(struct sysrq_state *sysrq,
 
 	default:
 		if (sysrq->active && value && value != 2) {
+			int from = sysrq->handle.dev->flags & INPUTDEV_FLAGS_SYNTHETIC ?
+					SYSRQ_FROM_SYNTHETIC : 0;
 			sysrq->need_reinject = false;
-			__handle_sysrq(sysrq_xlate[code], true);
+			__handle_sysrq(sysrq_xlate[code], from);
 		}
 		break;
 	}
@@ -1097,7 +1104,7 @@ static ssize_t write_sysrq_trigger(struct file *file, const char __user *buf,
 
 		if (get_user(c, buf))
 			return -EFAULT;
-		__handle_sysrq(c, false);
+		__handle_sysrq(c, SYSRQ_FROM_PROC);
 	}
 
 	return count;
diff --git a/include/linux/input.h b/include/linux/input.h
index fb5e23c7ed98..9d2b45a21ade 100644
--- a/include/linux/input.h
+++ b/include/linux/input.h
@@ -42,6 +42,7 @@ struct input_value {
  * @phys: physical path to the device in the system hierarchy
  * @uniq: unique identification code for the device (if device has it)
  * @id: id of the device (struct input_id)
+ * @flags: input device flags (SYNTHETIC, etc.)
  * @propbit: bitmap of device properties and quirks
  * @evbit: bitmap of types of events supported by the device (EV_KEY,
  *	EV_REL, etc.)
@@ -124,6 +125,8 @@ struct input_dev {
 	const char *uniq;
 	struct input_id id;
 
+	unsigned int flags;
+
 	unsigned long propbit[BITS_TO_LONGS(INPUT_PROP_CNT)];
 
 	unsigned long evbit[BITS_TO_LONGS(EV_CNT)];
@@ -190,6 +193,8 @@ struct input_dev {
 };
 #define to_input_dev(d) container_of(d, struct input_dev, dev)
 
+#define	INPUTDEV_FLAGS_SYNTHETIC	0x000000001
+
 /*
  * Verify that we are in sync with input_device_id mod_devicetable.h #defines
  */
diff --git a/include/linux/sysrq.h b/include/linux/sysrq.h
index 387fa7d05c98..f7c52a9ea394 100644
--- a/include/linux/sysrq.h
+++ b/include/linux/sysrq.h
@@ -28,6 +28,8 @@
 #define SYSRQ_ENABLE_BOOT	0x0080
 #define SYSRQ_ENABLE_RTNICE	0x0100
 
+#define SYSRQ_DISABLE_USERSPACE	0x00010000
+
 struct sysrq_key_op {
 	void (*handler)(int);
 	char *help_msg;
@@ -42,8 +44,12 @@ struct sysrq_key_op {
  * are available -- else NULL's).
  */
 
+#define SYSRQ_FROM_KERNEL	0x0001
+#define SYSRQ_FROM_PROC		0x0002
+#define SYSRQ_FROM_SYNTHETIC	0x0004
+
 void handle_sysrq(int key);
-void __handle_sysrq(int key, bool check_mask);
+void __handle_sysrq(int key, unsigned int from);
 int register_sysrq_key(int key, struct sysrq_key_op *op);
 int unregister_sysrq_key(int key, struct sysrq_key_op *op);
 struct sysrq_key_op *__sysrq_get_key_op(int key);
diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index c8146d53ca67..b480cadf9272 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -1970,7 +1970,7 @@ static int kdb_sr(int argc, const char **argv)
 		return KDB_ARGCOUNT;
 
 	kdb_trap_printk++;
-	__handle_sysrq(*argv[1], check_mask);
+	__handle_sysrq(*argv[1], check_mask ? SYSRQ_FROM_KERNEL : 0);
 	kdb_trap_printk--;
 
 	return 0;
diff --git a/security/Kconfig b/security/Kconfig
index 8e01fd59ae7e..4be6be71e075 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -213,6 +213,21 @@ config LOCK_DOWN_KERNEL
 	  turns off various features that might otherwise allow access to the
 	  kernel image (eg. setting MSR registers).
 
+config ALLOW_LOCKDOWN_LIFT
+	bool
+	help
+	  Allow the lockdown on a kernel to be lifted, thereby restoring the
+	  ability of userspace to access the kernel image (eg. by SysRq+x under
+	  x86).
+
+config ALLOW_LOCKDOWN_LIFT_BY_SYSRQ
+	bool "Allow the kernel lockdown to be lifted by SysRq"
+	depends on MAGIC_SYSRQ
+	help
+	  Allow the lockdown on a kernel to be lifted, by pressing a SysRq key
+	  combination on a wired keyboard.
+
+
 source security/selinux/Kconfig
 source security/smack/Kconfig
 source security/tomoyo/Kconfig
diff --git a/security/lock_down.c b/security/lock_down.c
index d8595c0e6673..f71118c340d2 100644
--- a/security/lock_down.c
+++ b/security/lock_down.c
@@ -11,8 +11,13 @@
 
 #include <linux/security.h>
 #include <linux/export.h>
+#include <linux/sysrq.h>
 
+#ifdef CONFIG_ALLOW_LOCKDOWN_LIFT
+static __read_mostly bool kernel_locked_down;
+#else
 static __ro_after_init bool kernel_locked_down;
+#endif
 
 /*
  * Put the kernel into lock-down mode.
@@ -58,3 +63,46 @@ bool __kernel_is_locked_down(const char *what, bool first)
 	return kernel_locked_down;
 }
 EXPORT_SYMBOL(__kernel_is_locked_down);
+
+/*
+ * Take the kernel out of lockdown mode.
+ */
+#ifdef CONFIG_ALLOW_LOCKDOWN_LIFT
+static void lift_kernel_lockdown(void)
+{
+	pr_notice("Lifting lockdown\n");
+	kernel_locked_down = false;
+}
+#endif
+
+/*
+ * Allow lockdown to be lifted by pressing something like SysRq+x (and not by
+ * echoing the appropriate letter into the sysrq-trigger file).
+ */
+#ifdef CONFIG_ALLOW_LOCKDOWN_LIFT_BY_KEY
+
+static void sysrq_handle_lockdown_lift(int key)
+{
+	if (kernel_locked_down)
+		lift_kernel_lockdown();
+}
+
+static struct sysrq_key_op lockdown_lift_sysrq_op = {
+	.handler	= sysrq_handle_lockdown_lift,
+	.help_msg	= "unSB(x)",
+	.action_msg	= "Disabling Secure Boot restrictions",
+	.enable_mask	= SYSRQ_DISABLE_USERSPACE,
+};
+
+static int __init lockdown_lift_sysrq(void)
+{
+	if (kernel_locked_down) {
+		lockdown_lift_sysrq_op.help_msg[5] = LOCKDOWN_LIFT_KEY;
+		register_sysrq_key(LOCKDOWN_LIFT_KEY, &lockdown_lift_sysrq_op);
+	}
+	return 0;
+}
+
+late_initcall(lockdown_lift_sysrq);
+
+#endif /* CONFIG_ALLOW_LOCKDOWN_LIFT_BY_KEY */

  parent reply index

Thread overview: 159+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-10-19 14:50 [PATCH 00/27] security, efi: Add " David Howells
2017-10-19 14:50 ` [PATCH 01/27] Add the ability to lock down access to the running kernel image David Howells
2017-10-20 23:19   ` James Morris
2017-10-19 14:50 ` David Howells [this message]
2017-10-19 17:20   ` [PATCH 02/27] Add a SysRq option to lift kernel lockdown Randy Dunlap
2017-10-19 22:12   ` David Howells
2017-11-07 17:39   ` Thiago Jung Bauermann
2017-11-07 22:56   ` David Howells
2017-10-19 14:50 ` [PATCH 03/27] Enforce module signatures if the kernel is locked down David Howells
2017-10-20  6:33   ` joeyli
2017-10-20 23:21   ` James Morris
2017-10-27 18:48   ` Mimi Zohar
2017-10-30 17:00   ` David Howells
2017-10-30 17:52     ` Mimi Zohar
2017-11-02 17:22   ` David Howells
2017-11-02 19:13     ` Mimi Zohar
2017-11-02 21:30     ` David Howells
2017-11-02 21:41       ` Mimi Zohar
2017-11-02 22:01       ` David Howells
2017-11-02 22:18         ` Mimi Zohar
2017-10-19 14:51 ` [PATCH 04/27] Restrict /dev/mem and /dev/kmem when " David Howells
2017-10-20  6:37   ` joeyli
2017-10-20 23:21   ` James Morris
2017-10-19 14:51 ` [PATCH 05/27] kexec: Disable at runtime if " David Howells
2017-10-20  6:38   ` joeyli
2017-10-20 23:22   ` James Morris
2017-10-19 14:51 ` [PATCH 06/27] Copy secure_boot flag in boot params across kexec reboot David Howells
2017-10-20  6:40   ` joeyli
2017-10-19 14:51 ` [PATCH 07/27] kexec_file: Disable at runtime if securelevel has been set David Howells
2017-10-20 23:26   ` James Morris
2017-10-23 15:54   ` Mimi Zohar
2017-10-26  7:42     ` joeyli
2017-10-26 14:17       ` Mimi Zohar
2017-10-27 19:30         ` Mimi Zohar
2017-10-27 19:32         ` Mimi Zohar
2017-10-28  8:34           ` joeyli
2017-10-29 22:26             ` Mimi Zohar
2017-10-30  9:00       ` David Howells
2017-10-30 12:01         ` Mimi Zohar
2017-10-26 15:02     ` David Howells
2017-10-26 15:46       ` Mimi Zohar
2017-10-30 15:49       ` David Howells
2017-10-30 16:43         ` Mimi Zohar
2017-11-02 17:00         ` David Howells
2017-10-26 14:51   ` David Howells
2017-11-02 17:29   ` David Howells
2017-10-19 14:51 ` [PATCH 08/27] hibernate: Disable when the kernel is locked down David Howells
2017-10-20  6:40   ` joeyli
2017-10-19 14:51 ` [PATCH 09/27] uswsusp: " David Howells
2017-10-20  6:41   ` joeyli
2017-10-20 23:29   ` James Morris
2017-10-19 14:51 ` [PATCH 10/27] PCI: Lock down BAR access " David Howells
2017-10-20  6:42   ` joeyli
2017-10-19 14:51 ` [PATCH 11/27] x86: Lock down IO port " David Howells
2017-10-20  6:43   ` joeyli
2017-10-19 14:52 ` [PATCH 12/27] x86/msr: Restrict MSR " David Howells
2017-10-20  6:43   ` joeyli
2017-10-20 18:09   ` Alan Cox
2017-10-20 20:48   ` David Howells
2017-10-21  4:39     ` joeyli
2017-10-23 14:49   ` David Howells
2017-10-25 14:03     ` joeyli
2017-10-19 14:52 ` [PATCH 13/27] asus-wmi: Restrict debugfs interface " David Howells
2017-10-20  6:44   ` joeyli
2017-10-19 14:52 ` [PATCH 14/27] ACPI: Limit access to custom_method " David Howells
2017-10-20  6:45   ` joeyli
2017-10-19 14:52 ` [PATCH 15/27] acpi: Ignore acpi_rsdp kernel param when the kernel has been " David Howells
2017-10-20  6:45   ` joeyli
2017-10-19 14:52 ` [PATCH 16/27] acpi: Disable ACPI table override if the kernel is " David Howells
2017-10-20  6:46   ` joeyli
2017-10-19 14:52 ` [PATCH 17/27] acpi: Disable APEI error injection " David Howells
2017-10-20  6:47   ` joeyli
2017-10-19 14:52 ` [PATCH 18/27] bpf: Restrict kernel image access functions when " David Howells
2017-10-19 22:18   ` Alexei Starovoitov
2017-10-20  2:47     ` joeyli
2017-10-20  8:08     ` David Howells
2017-10-20 15:57       ` jlee
2017-10-20 23:00         ` Alexei Starovoitov
2017-10-23 14:51         ` David Howells
2017-10-20 16:03       ` David Howells
2017-10-20 16:43         ` jlee
2017-10-23 14:53         ` David Howells
2017-10-25  7:07           ` joeyli
2017-10-19 22:48   ` David Howells
2017-10-19 23:31     ` Alexei Starovoitov
2017-11-09 17:15     ` David Howells
2017-10-19 14:52 ` [PATCH 19/27] scsi: Lock down the eata driver David Howells
2017-10-19 14:53 ` [PATCH 20/27] Prohibit PCMCIA CIS storage when the kernel is locked down David Howells
2017-10-19 14:53 ` [PATCH 21/27] Lock down TIOCSSERIAL David Howells
2017-10-19 14:53 ` [PATCH 22/27] Lock down module params that specify hardware parameters (eg. ioport) David Howells
2017-10-19 14:53 ` [PATCH 23/27] x86/mmiotrace: Lock down the testmmiotrace module David Howells
2017-10-19 14:53 ` [PATCH 24/27] debugfs: Disallow use of debugfs files when the kernel is locked down David Howells
2017-10-19 14:53 ` [PATCH 25/27] Lock down /proc/kcore David Howells
2017-10-21  2:11   ` James Morris
2017-10-23 14:56   ` David Howells
2017-10-19 14:53 ` [PATCH 26/27] efi: Add an EFI_SECURE_BOOT flag to indicate secure boot mode David Howells
2017-10-21  2:19   ` James Morris
2017-10-23 14:58   ` David Howells
2017-10-19 14:53 ` [PATCH 27/27] efi: Lock down the kernel if booted in " David Howells
2017-10-19 22:39 ` [PATCH 00/27] security, efi: Add kernel lockdown David Howells
2017-10-23 14:34 ` [PATCH 04/27] Restrict /dev/mem and /dev/kmem when the kernel is locked down David Howells
2017-10-24 10:48   ` Ethan Zhao
2017-10-24 14:56   ` David Howells
2017-11-02 22:01 ` [PATCH 00/27] security, efi: Add kernel lockdown Mimi Zohar
2017-11-02 22:04 ` Firmware signing -- " David Howells
2017-11-02 22:10   ` Mimi Zohar
2017-11-07 23:07     ` Luis R. Rodriguez
2017-11-08  6:15       ` AKASHI, Takahiro
2017-11-08 19:46         ` Luis R. Rodriguez
2017-11-09  1:48           ` AKASHI, Takahiro
2017-11-09  2:17             ` Mimi Zohar
2017-11-09  4:46               ` AKASHI, Takahiro
2017-11-10 13:37                 ` Mimi Zohar
2017-11-11  2:32                 ` Alan Cox
2017-11-13 11:49                   ` Mimi Zohar
2017-11-13 17:42                   ` Luis R. Rodriguez
2017-11-13 21:08                     ` Alan Cox
2017-12-04 19:51                       ` Luis R. Rodriguez
2017-12-07 15:32                         ` Alan Cox
2017-11-13 21:44                     ` David Howells
2017-11-13 22:09                       ` Linus Torvalds
2017-11-14  0:20                         ` Alan Cox
2017-11-14 12:21                         ` Mimi Zohar
2017-11-14 12:38                           ` Greg Kroah-Hartman
2017-11-14 13:17                             ` Mimi Zohar
2017-11-14 17:34                           ` Linus Torvalds
2017-11-14 19:58                             ` Matthew Garrett
2017-11-14 20:18                               ` Linus Torvalds
2017-11-14 20:31                                 ` Matthew Garrett
2017-11-14 20:35                                   ` Linus Torvalds
2017-11-14 20:37                                     ` Matthew Garrett
2017-11-14 20:50                                 ` Luis R. Rodriguez
2017-11-14 20:55                                   ` Matthew Garrett
2017-11-14 22:14                                     ` James Bottomley
2017-11-14 22:17                                       ` Matthew Garrett
2017-11-14 22:31                                         ` James Bottomley
2017-11-14 22:34                                           ` Matthew Garrett
2017-11-15 11:49                                   ` Mimi Zohar
2017-11-15 17:52                                     ` Luis R. Rodriguez
2017-11-15 19:56                                       ` Mimi Zohar
2017-11-15 20:46                                         ` Luis R. Rodriguez
2017-11-16  0:05                                           ` Mimi Zohar
2017-12-05 10:27                                 ` Pavel Machek
2017-12-07 23:02                                   ` Luis R. Rodriguez
2017-12-08 17:11                                     ` Alan Cox
2017-11-10  1:46             ` Luis R. Rodriguez
2017-11-10 13:45               ` Mimi Zohar
2017-11-13 18:50                 ` Luis R. Rodriguez
2017-11-13 19:08                   ` Luis R. Rodriguez
2017-11-08 20:01       ` Mimi Zohar
2017-11-08 20:09         ` Luis R. Rodriguez
2019-02-28 21:28 [PULL REQUEST] Lock down patches Matthew Garrett
2019-02-28 22:44 ` [PATCH 01/27] Add the ability to lock down access to the running kernel image Matthew Garrett
2019-02-28 22:44   ` [PATCH 02/27] Add a SysRq option to lift kernel lockdown Matthew Garrett
2019-02-28 23:10 ` [PATCH 01/27] Add the ability to lock down access to the running kernel image Matthew Garrett
2019-02-28 23:10   ` [PATCH 02/27] Add a SysRq option to lift kernel lockdown Matthew Garrett
2019-02-28 23:11 ` [PATCH 01/27] Add the ability to lock down access to the running kernel image Matthew Garrett
2019-02-28 23:11   ` [PATCH 02/27] Add a SysRq option to lift kernel lockdown Matthew Garrett
2019-02-28 23:11 ` [PATCH 01/27] Add the ability to lock down access to the running kernel image Matthew Garrett
2019-02-28 23:11   ` [PATCH 02/27] Add a SysRq option to lift kernel lockdown Matthew Garrett
2019-03-06 23:58 [PULL REQUEST] Kernel lockdown patches for 5.2 Matthew Garrett
2019-03-06 23:58 ` [PATCH 02/27] Add a SysRq option to lift kernel lockdown Matthew Garrett
2019-03-07  0:09   ` Randy Dunlap
2019-03-07  0:12     ` Matthew Garrett
2019-03-07 15:59 ` David Howells

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	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
	git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git
	git clone --mirror https://lore.kernel.org/lkml/9 lkml/git/9.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git