linux-kernel - [PATCH] pstore: honor dmesg_restrict sysctl on dmesg dumps

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Message-ID: <20141019180515.GA14661@moniac.lan.yath.de>
Date:	Sun, 19 Oct 2014 20:05:15 +0200
From:	Sebastian Schmidt <yath@...h.de>
To:	Anton Vorontsov <anton@...msg.org>,
	Colin Cross <ccross@...roid.com>,
	Kees Cook <keescook@...omium.org>,
	Tony Luck <tony.luck@...el.com>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] pstore: honor dmesg_restrict sysctl on dmesg dumps

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@...h.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

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