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Message-Id: <1453502345-30416-2-git-send-email-keescook@chromium.org>
Date: Fri, 22 Jan 2016 14:39:04 -0800
From: Kees Cook <keescook@...omium.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Kees Cook <keescook@...omium.org>,
Al Viro <viro@...iv.linux.org.uk>,
Richard Weinberger <richard@....at>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Andy Lutomirski <luto@...capital.net>,
Robert Święcki <robert@...ecki.net>,
Dmitry Vyukov <dvyukov@...gle.com>,
David Howells <dhowells@...hat.com>,
Miklos Szeredi <mszeredi@...e.cz>,
Kostya Serebryany <kcc@...gle.com>,
Alexander Potapenko <glider@...gle.com>,
Eric Dumazet <edumazet@...gle.com>,
Sasha Levin <sasha.levin@...cle.com>,
linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
kernel-hardening@...ts.openwall.com
Subject: [PATCH 1/2] sysctl: expand use of proc_dointvec_minmax_sysadmin
Several sysctls expect a state where the highest value (in extra2) is
locked once set for that boot. Yama does this, and kptr_restrict should
be doing it. This extracts Yama's logic and adds it to the existing
proc_dointvec_minmax_sysadmin, taking care to avoid the simple boolean
states (which do not get locked). Since Yama wants to be checking a
different capability, we build wrappers for both cases (CAP_SYS_ADMIN
and CAP_SYS_PTRACE).
Signed-off-by: Kees Cook <keescook@...omium.org>
---
Documentation/sysctl/kernel.txt | 4 +++-
include/linux/sysctl.h | 18 ++++++++++++++++++
kernel/sysctl.c | 34 +++++++++++++++++++++-------------
security/yama/yama_lsm.c | 18 +-----------------
4 files changed, 43 insertions(+), 31 deletions(-)
diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index 73c6b1ef0e84..bbfc5e339a3d 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -385,7 +385,9 @@ to protect against uses of %pK in dmesg(8) if leaking kernel pointer
values to unprivileged users is a concern.
When kptr_restrict is set to (2), kernel pointers printed using
-%pK will be replaced with 0's regardless of privileges.
+%pK will be replaced with 0's regardless of privileges, and the value
+will be locked at "2", so that the root user cannot remove this
+restriction.
==============================================================
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index fa7bc29925c9..f8f0b991fe3e 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -23,6 +23,7 @@
#include <linux/list.h>
#include <linux/rcupdate.h>
+#include <linux/capability.h>
#include <linux/wait.h>
#include <linux/rbtree.h>
#include <uapi/linux/sysctl.h>
@@ -55,6 +56,23 @@ extern int proc_doulongvec_ms_jiffies_minmax(struct ctl_table *table, int,
void __user *, size_t *, loff_t *);
extern int proc_do_large_bitmap(struct ctl_table *, int,
void __user *, size_t *, loff_t *);
+extern int proc_dointvec_minmax_cap(int cap, struct ctl_table *table,
+ int write, void __user *buffer,
+ size_t *lenp, loff_t *ppos);
+static inline int proc_dointvec_minmax_cap_sysadmin(struct ctl_table *table,
+ int write, void __user *buffer,
+ size_t *lenp, loff_t *ppos)
+{
+ return proc_dointvec_minmax_cap(CAP_SYS_ADMIN, table, write, buffer,
+ lenp, ppos);
+}
+static inline int proc_dointvec_minmax_cap_ptrace(struct ctl_table *table,
+ int write, void __user *buffer,
+ size_t *lenp, loff_t *ppos)
+{
+ return proc_dointvec_minmax_cap(CAP_SYS_PTRACE, table, write, buffer,
+ lenp, ppos);
+}
/*
* Register a set of sysctl names by calling register_sysctl_table
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index c810f8afdb7f..fc8899dd636d 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -181,11 +181,6 @@ static int proc_taint(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp, loff_t *ppos);
#endif
-#ifdef CONFIG_PRINTK
-static int proc_dointvec_minmax_sysadmin(struct ctl_table *table, int write,
- void __user *buffer, size_t *lenp, loff_t *ppos);
-#endif
-
static int proc_dointvec_minmax_coredump(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp, loff_t *ppos);
#ifdef CONFIG_COREDUMP
@@ -803,7 +798,7 @@ static struct ctl_table kern_table[] = {
.data = &dmesg_restrict,
.maxlen = sizeof(int),
.mode = 0644,
- .proc_handler = proc_dointvec_minmax_sysadmin,
+ .proc_handler = proc_dointvec_minmax_cap_sysadmin,
.extra1 = &zero,
.extra2 = &one,
},
@@ -812,7 +807,7 @@ static struct ctl_table kern_table[] = {
.data = &kptr_restrict,
.maxlen = sizeof(int),
.mode = 0644,
- .proc_handler = proc_dointvec_minmax_sysadmin,
+ .proc_handler = proc_dointvec_minmax_cap_sysadmin,
.extra1 = &zero,
.extra2 = &two,
},
@@ -2217,16 +2212,29 @@ static int proc_taint(struct ctl_table *table, int write,
return err;
}
-#ifdef CONFIG_PRINTK
-static int proc_dointvec_minmax_sysadmin(struct ctl_table *table, int write,
- void __user *buffer, size_t *lenp, loff_t *ppos)
+int proc_dointvec_minmax_cap(int cap, struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp, loff_t *ppos)
{
- if (write && !capable(CAP_SYS_ADMIN))
+ struct ctl_table table_copy;
+ int value;
+
+ /* Require init capabilities to make changes. */
+ if (write && !capable(cap))
return -EPERM;
- return proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+ /*
+ * To deal with const sysctl tables, we make a copy to perform
+ * the locking. When data is >1 and ==extra2, lock extra1 to
+ * extra2 to stop the value from being changed any further at
+ * runtime.
+ */
+ table_copy = *table;
+ value = *(int *)table_copy.data;
+ if (value > 1 && value == *(int *)table_copy.extra2)
+ table_copy.extra1 = table_copy.extra2;
+
+ return proc_dointvec_minmax(&table_copy, write, buffer, lenp, ppos);
}
-#endif
struct do_proc_dointvec_minmax_conv_param {
int *min;
diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c
index d3c19c970a06..3215afd08fbd 100644
--- a/security/yama/yama_lsm.c
+++ b/security/yama/yama_lsm.c
@@ -354,22 +354,6 @@ static struct security_hook_list yama_hooks[] = {
};
#ifdef CONFIG_SYSCTL
-static int yama_dointvec_minmax(struct ctl_table *table, int write,
- void __user *buffer, size_t *lenp, loff_t *ppos)
-{
- struct ctl_table table_copy;
-
- if (write && !capable(CAP_SYS_PTRACE))
- return -EPERM;
-
- /* Lock the max value if it ever gets set. */
- table_copy = *table;
- if (*(int *)table_copy.data == *(int *)table_copy.extra2)
- table_copy.extra1 = table_copy.extra2;
-
- return proc_dointvec_minmax(&table_copy, write, buffer, lenp, ppos);
-}
-
static int zero;
static int max_scope = YAMA_SCOPE_NO_ATTACH;
@@ -385,7 +369,7 @@ static struct ctl_table yama_sysctl_table[] = {
.data = &ptrace_scope,
.maxlen = sizeof(int),
.mode = 0644,
- .proc_handler = yama_dointvec_minmax,
+ .proc_handler = proc_dointvec_minmax_cap_ptrace,
.extra1 = &zero,
.extra2 = &max_scope,
},
--
2.6.3
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