[PATCH V40 21/29] lockdown: Lock down /proc/kcore

[Matthew Garrett]

From: David Howells <dhowe...@redhat.com>

Disallow access to /proc/kcore when the kernel is locked down to prevent
access to cryptographic data. This is limited to lockdown
confidentiality mode and is still permitted in integrity mode.

Signed-off-by: David Howells <dhowe...@redhat.com>
Signed-off-by: Matthew Garrett <mj...@google.com>
Reviewed-by: Kees Cook <keesc...@chromium.org>
Signed-off-by: James Morris <jmor...@namei.org>
---
 fs/proc/kcore.c              | 5 +++++
 include/linux/security.h     | 1 +
 security/lockdown/lockdown.c | 1 +
 3 files changed, 7 insertions(+)

diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index f5834488b67d..ee2c576cc94e 100644
--- a/fs/proc/kcore.c
+++ b/fs/proc/kcore.c
@@ -31,6 +31,7 @@
 #include <linux/ioport.h>
 #include <linux/memory.h>
 #include <linux/sched/task.h>
+#include <linux/security.h>
 #include <asm/sections.h>
 #include "internal.h"
 
@@ -545,6 +546,10 @@ read_kcore(struct file *file, char __user *buffer, size_t 
buflen, loff_t *fpos)
 
 static int open_kcore(struct inode *inode, struct file *filp)
 {
+       int ret = security_locked_down(LOCKDOWN_KCORE);
+
+       if (ret)
+               return ret;
        if (!capable(CAP_SYS_RAWIO))
                return -EPERM;
 
diff --git a/include/linux/security.h b/include/linux/security.h
index d8db7ea4c4bf..669e8de5299d 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -116,6 +116,7 @@ enum lockdown_reason {
        LOCKDOWN_MODULE_PARAMETERS,
        LOCKDOWN_MMIOTRACE,
        LOCKDOWN_INTEGRITY_MAX,
+       LOCKDOWN_KCORE,
        LOCKDOWN_CONFIDENTIALITY_MAX,
 };
 
diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
index 2eadbe0667e7..403b30357f75 100644
--- a/security/lockdown/lockdown.c
+++ b/security/lockdown/lockdown.c
@@ -31,6 +31,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] 
= {
        [LOCKDOWN_MODULE_PARAMETERS] = "unsafe module parameters",
        [LOCKDOWN_MMIOTRACE] = "unsafe mmio",
        [LOCKDOWN_INTEGRITY_MAX] = "integrity",
+       [LOCKDOWN_KCORE] = "/proc/kcore access",
        [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
 };
 
-- 
2.23.0.rc1.153.gdeed80330f-goog