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@yath.de>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Tony Luck <tony.luck@intel.com>

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,