Re: [PATCH v3 11/34] lsm: get rid of the lsm_names list and do some cleanup

[Paul Moore]

On Thu, Sep 4, 2025 at 11:18 AM Paul Moore <p...@paul-moore.com> wrote:
>
> I'll rework this function, but I'll hold off on posting another
> revision until I hear back on some of the reviews that are still
> pending in case additional edits are needed.

For the curious, here is what it looks like now:

diff --git a/security/inode.c b/security/inode.c
index 43382ef8896e..4813d116fd7c 100644
--- a/security/inode.c
+++ b/security/inode.c
@@ -22,6 +22,8 @@
#include <linux/lsm_hooks.h>
#include <linux/magic.h>

+#include "lsm.h"
+
static struct vfsmount *mount;
static int mount_count;

@@ -315,12 +317,49 @@ void securityfs_remove(struct dentry *dentry)
EXPORT_SYMBOL_GPL(securityfs_remove);

#ifdef CONFIG_SECURITY
+#include <linux/spinlock.h>
+
static struct dentry *lsm_dentry;
+
static ssize_t lsm_read(struct file *filp, char __user *buf, size_t count,
                       loff_t *ppos)
{
-       return simple_read_from_buffer(buf, count, ppos, lsm_names,
-               strlen(lsm_names));
+       int i;
+       static char *str;
+       static size_t len;
+       static DEFINE_SPINLOCK(lock);
+
+       /* NOTE: we never free or modify the string once it is set */
+
+       if (unlikely(!str)) {
+               char *str_tmp;
+               size_t len_tmp = 0;
+
+               for (i = 0; i < lsm_active_cnt; i++)
+                       /* the '+ 1' accounts for either a comma or a NUL */
+                       len_tmp += strlen(lsm_idlist[i]->name) + 1;
+
+               str_tmp = kmalloc(len_tmp, GFP_KERNEL);
+               if (!str_tmp)
+                       return -ENOMEM;
+               str_tmp[0] = '\0';
+
+               for (i = 0; i < lsm_active_cnt; i++) {
+                       if (i > 0)
+                               strcat(str_tmp, ",");
+                       strcat(str_tmp, lsm_idlist[i]->name);
+               }
+
+               spin_lock(&lock);
+               if (!str) {
+                       str = str_tmp;
+                       len = len_tmp - 1;
+               } else
+                       kfree(str_tmp);
+               spin_unlock(&lock);
+       }
+
+       return simple_read_from_buffer(buf, count, ppos, str, len);
}

-- 
paul-moore.com