Re: [PATCH 2/2] sysctl: Restore the selinux path based label lookup for sysctls.

[ebiederm@xmission.com (Eric W. Biederman)]

Stephen Smalley <sds@tycho.nsa.gov> writes:

> Actually, on further inspection, it looks like the real issue is the
> "path" name generation; "cat /proc/sys/kernel/modprobe" yields a call to
> security_genfs_sid() with just "/modprobe" rather than the expected
> "/sys/kernel/modprobe".  Which likewise leaves us with the generic proc
> label, just as with the inode permission check, so I end up seeing
> checks against it only.

Ok.  It looks like two silly thing are going on here.
I failed to register the root sysctl table, so none of the parent
pointers got set.

I didn't prepend /sys in the compatibility code, so for something with
the parent pointers set you would have gotten "/kernel/modprobe" instead
of /sys/kernel/modprobe"

Sorry about that.

I think the patch below will fix it.

Eric

diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 24f36f1..f316854 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -929,8 +929,6 @@ extern struct ctl_table_header *sysctl_head_next(struct ctl_table_header *prev);
 extern void sysctl_head_finish(struct ctl_table_header *prev);
 extern int sysctl_perm(struct ctl_table *table, int op);
 
-extern void sysctl_init(void);
-
 typedef struct ctl_table ctl_table;
 
 typedef int ctl_handler (ctl_table *table, int __user *name, int nlen,
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 0a5499f..0bb2c5f 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1241,6 +1241,14 @@ static void sysctl_set_parent(struct ctl_table *parent, struct ctl_table *table)
 	}
 }
 
+static __init int sysctl_init(void)
+{
+	sysctl_set_parent(NULL, root_table);
+	return 0;
+}
+
+core_initcall(sysctl_init);
+
 /**
  * register_sysctl_table - register a sysctl hierarchy
  * @table: the top-level table structure
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index c17a8dd..aad2697 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1452,6 +1452,12 @@ static int selinux_sysctl_get_sid(ctl_table *table, u16 tclass, u32 *sid)
 		path = end;
 		table = table->parent;
 	}
+	buflen -= 4;
+	if (buflen < 0)
+		goto out_free;
+	end -= 4;
+	memcpy(end, "/sys", 4);
+	path = end;
 	rc = security_genfs_sid("proc", path, tclass, sid);
 out_free:
 	free_page((unsigned long)buffer);