Discussion:
[PATCH] pstore: honor dmesg_restrict sysctl on dmesg dumps
(too old to reply)
Sebastian Schmidt
2014-10-19 18:05:15 UTC
Permalink
When the kernel.dmesg_restrict restriction is in place, only users with
CAP_SYSLOG should be able to access crash dumps (like: attacker is
trying to exploit a bug, watchdog reboots, attacker can happily read
crash dumps and logs).

This puts the restriction on console-* types as well as sensitive
information could have been leaked there.

Other log types are unaffected.

Signed-off-by: Sebastian Schmidt <***@yath.de>
---
fs/pstore/inode.c | 22 ++++++++++++++++++++++
include/linux/syslog.h | 1 +
kernel/printk/printk.c | 2 +-
3 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/fs/pstore/inode.c b/fs/pstore/inode.c
index fafb7a0..5041660 100644
--- a/fs/pstore/inode.c
+++ b/fs/pstore/inode.c
@@ -36,6 +36,7 @@
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/uaccess.h>
+#include <linux/syslog.h>

#include "internal.h"

@@ -120,6 +121,18 @@ static const struct seq_operations pstore_ftrace_seq_ops = {
.show = pstore_ftrace_seq_show,
};

+static int pstore_check_syslog_permissions(struct pstore_private *ps)
+{
+ switch (ps->type) {
+ case PSTORE_TYPE_DMESG:
+ case PSTORE_TYPE_CONSOLE:
+ return check_syslog_permissions(SYSLOG_ACTION_READ_ALL,
+ SYSLOG_FROM_READER);
+ default:
+ return 0;
+ }
+}
+
static ssize_t pstore_file_read(struct file *file, char __user *userbuf,
size_t count, loff_t *ppos)
{
@@ -138,6 +151,10 @@ static int pstore_file_open(struct inode *inode, struct file *file)
int err;
const struct seq_operations *sops = NULL;

+ err = pstore_check_syslog_permissions(ps);
+ if (err)
+ return err;
+
if (ps->type == PSTORE_TYPE_FTRACE)
sops = &pstore_ftrace_seq_ops;

@@ -174,6 +191,11 @@ static const struct file_operations pstore_file_operations = {
static int pstore_unlink(struct inode *dir, struct dentry *dentry)
{
struct pstore_private *p = dentry->d_inode->i_private;
+ int err;
+
+ err = pstore_check_syslog_permissions(p);
+ if (err)
+ return err;

if (p->psi->erase)
p->psi->erase(p->type, p->id, p->count,
diff --git a/include/linux/syslog.h b/include/linux/syslog.h
index 98a3153..9def529 100644
--- a/include/linux/syslog.h
+++ b/include/linux/syslog.h
@@ -48,5 +48,6 @@
#define SYSLOG_FROM_PROC 1

int do_syslog(int type, char __user *buf, int count, bool from_file);
+int check_syslog_permissions(int type, bool from_file);

#endif /* _LINUX_SYSLOG_H */
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index ced2b84..c8755e7 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -480,7 +480,7 @@ static int syslog_action_restricted(int type)
type != SYSLOG_ACTION_SIZE_BUFFER;
}

-static int check_syslog_permissions(int type, bool from_file)
+int check_syslog_permissions(int type, bool from_file)
{
/*
* If this is from /proc/kmsg and we've already opened it, then we've
--
2.1.1
Kees Cook
2014-10-20 18:15:57 UTC
Permalink
Post by Sebastian Schmidt
When the kernel.dmesg_restrict restriction is in place, only users with
CAP_SYSLOG should be able to access crash dumps (like: attacker is
trying to exploit a bug, watchdog reboots, attacker can happily read
crash dumps and logs).
This puts the restriction on console-* types as well as sensitive
information could have been leaked there.
Other log types are unaffected.
This looks sensible to me; thanks!

Acked-by: Kees Cook <***@chromium.org>

-Kees
Post by Sebastian Schmidt
---
fs/pstore/inode.c | 22 ++++++++++++++++++++++
include/linux/syslog.h | 1 +
kernel/printk/printk.c | 2 +-
3 files changed, 24 insertions(+), 1 deletion(-)
diff --git a/fs/pstore/inode.c b/fs/pstore/inode.c
index fafb7a0..5041660 100644
--- a/fs/pstore/inode.c
+++ b/fs/pstore/inode.c
@@ -36,6 +36,7 @@
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/uaccess.h>
+#include <linux/syslog.h>
#include "internal.h"
@@ -120,6 +121,18 @@ static const struct seq_operations pstore_ftrace_seq_ops = {
.show = pstore_ftrace_seq_show,
};
+static int pstore_check_syslog_permissions(struct pstore_private *ps)
+{
+ switch (ps->type) {
+ return check_syslog_permissions(SYSLOG_ACTION_READ_ALL,
+ SYSLOG_FROM_READER);
+ return 0;
+ }
+}
+
static ssize_t pstore_file_read(struct file *file, char __user *userbuf,
size_t count, loff_t *ppos)
{
@@ -138,6 +151,10 @@ static int pstore_file_open(struct inode *inode, struct file *file)
int err;
const struct seq_operations *sops = NULL;
+ err = pstore_check_syslog_permissions(ps);
+ if (err)
+ return err;
+
if (ps->type == PSTORE_TYPE_FTRACE)
sops = &pstore_ftrace_seq_ops;
@@ -174,6 +191,11 @@ static const struct file_operations pstore_file_operations = {
static int pstore_unlink(struct inode *dir, struct dentry *dentry)
{
struct pstore_private *p = dentry->d_inode->i_private;
+ int err;
+
+ err = pstore_check_syslog_permissions(p);
+ if (err)
+ return err;
if (p->psi->erase)
p->psi->erase(p->type, p->id, p->count,
diff --git a/include/linux/syslog.h b/include/linux/syslog.h
index 98a3153..9def529 100644
--- a/include/linux/syslog.h
+++ b/include/linux/syslog.h
@@ -48,5 +48,6 @@
#define SYSLOG_FROM_PROC 1
int do_syslog(int type, char __user *buf, int count, bool from_file);
+int check_syslog_permissions(int type, bool from_file);
#endif /* _LINUX_SYSLOG_H */
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index ced2b84..c8755e7 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -480,7 +480,7 @@ static int syslog_action_restricted(int type)
type != SYSLOG_ACTION_SIZE_BUFFER;
}
-static int check_syslog_permissions(int type, bool from_file)
+int check_syslog_permissions(int type, bool from_file)
{
/*
* If this is from /proc/kmsg and we've already opened it, then we've
--
2.1.1
--
Kees Cook
Chrome OS Security
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