On 8/14/25 15:50, Paul Moore wrote:
The LSM currently has a lot of code to maintain a list of the currently
active LSMs in a human readable string, with the only user being the
"/sys/kernel/security/lsm" code. Let's drop all of that code and
generate the string on first use and then cache it for subsequent use.
Signed-off-by: Paul Moore <p...@paul-moore.com>
---
include/linux/lsm_hooks.h | 1 -
security/inode.c | 59 +++++++++++++++++++++++++++++++++++++--
security/lsm_init.c | 49 --------------------------------
3 files changed, 57 insertions(+), 52 deletions(-)
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 7343dd60b1d5..65a8227bece7 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -172,7 +172,6 @@ struct lsm_info {
/* DO NOT tamper with these variables outside of the LSM framework */
-extern char *lsm_names;
extern struct lsm_static_calls_table static_calls_table __ro_after_init;
/**
diff --git a/security/inode.c b/security/inode.c
index 43382ef8896e..a5e7a073e672 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 +317,65 @@ void securityfs_remove(struct dentry *dentry)
EXPORT_SYMBOL_GPL(securityfs_remove);
#ifdef CONFIG_SECURITY
+#include <linux/spinlock.h>
+
static struct dentry *lsm_dentry;
+
+/* NOTE: we never free the string below once it is set. */
+static DEFINE_SPINLOCK(lsm_read_lock);
nit, this is only used on the write side, so not the best name
+static char *lsm_read_str = NULL;
+static ssize_t lsm_read_len = 0;
+
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;
+ char *str;
+ ssize_t len;
+
+restart:
+
+ rcu_read_lock();
+ if (!lsm_read_str) {
should probably be
if (!rcu_access_pointer(lsm_read_str)) {
+ /* we need to generate the string and try again */
+ rcu_read_unlock();
+ goto generate_string;
+ }
+ len = simple_read_from_buffer(buf, count, ppos,
+ rcu_dereference(lsm_read_str),
+ lsm_read_len);
+ rcu_read_unlock();
+ return len;
+
+generate_string:
+
+ for (i = 0; i < lsm_active_cnt; i++)
+ /* the '+ 1' accounts for either a comma or a NUL */
+ len += strlen(lsm_idlist[i]->name) + 1;
+
+ str = kmalloc(len, GFP_KERNEL);
+ if (!str)
+ return -ENOMEM;
+ str[0] = '\0';
+
+ for (i = 0; i < lsm_active_cnt; i++) {
+ if (i > 0)
+ strcat(str, ",");
+ strcat(str, lsm_idlist[i]->name);
+ }
+
+ spin_lock(&lsm_read_lock);
+ if (lsm_read_str) {
+ /* we raced and lost */
+ spin_unlock(&lsm_read_lock);
+ kfree(str);
+ goto restart;
+ }
+ lsm_read_str = str;
+ lsm_read_len = len - 1;
+ spin_unlock(&lsm_read_lock);
+
+ goto restart;
}
static const struct file_operations lsm_ops = {
diff --git a/security/lsm_init.c b/security/lsm_init.c
index 9e495a36a332..87e2147016b3 100644
--- a/security/lsm_init.c
+++ b/security/lsm_init.c
@@ -10,8 +10,6 @@
#include "lsm.h"
-char *lsm_names;
-
/* Pointers to LSM sections defined in include/asm-generic/vmlinux.lds.h */
extern struct lsm_info __start_lsm_info[], __end_lsm_info[];
extern struct lsm_info __start_early_lsm_info[], __end_early_lsm_info[];
@@ -371,42 +369,6 @@ static void __init lsm_init_ordered(void)
}
}
-static bool match_last_lsm(const char *list, const char *lsm)
-{
- const char *last;
-
- if (WARN_ON(!list || !lsm))
- return false;
- last = strrchr(list, ',');
- if (last)
- /* Pass the comma, strcmp() will check for '\0' */
- last++;
- else
- last = list;
- return !strcmp(last, lsm);
-}
-
-static int lsm_append(const char *new, char **result)
-{
- char *cp;
-
- if (*result == NULL) {
- *result = kstrdup(new, GFP_KERNEL);
- if (*result == NULL)
- return -ENOMEM;
- } else {
- /* Check if it is the last registered name */
- if (match_last_lsm(*result, new))
- return 0;
- cp = kasprintf(GFP_KERNEL, "%s,%s", *result, new);
- if (cp == NULL)
- return -ENOMEM;
- kfree(*result);
- *result = cp;
- }
- return 0;
-}
-
static void __init lsm_static_call_init(struct security_hook_list *hl)
{
struct lsm_static_call *scall = hl->scalls;
@@ -443,15 +405,6 @@ void __init security_add_hooks(struct security_hook_list
*hooks, int count,
hooks[i].lsmid = lsmid;
lsm_static_call_init(&hooks[i]);
}
-
- /*
- * Don't try to append during early_security_init(), we'll come back
- * and fix this up afterwards.
- */
- if (slab_is_available()) {
- if (lsm_append(lsmid->name, &lsm_names) < 0)
- panic("%s - Cannot get early memory.\n", __func__);
- }
}
int __init early_security_init(void)
@@ -488,8 +441,6 @@ int __init security_init(void)
lsm_early_for_each_raw(lsm) {
init_debug(" early started: %s (%s)\n", lsm->id->name,
is_enabled(lsm) ? "enabled" : "disabled");
- if (lsm->enabled)
- lsm_append(lsm->id->name, &lsm_names);
}
/* Load LSMs in specified order. */
