Re: [PATCH v4 11/34] lsm: get rid of the lsm_names list and do some cleanup

[Mimi Zohar <zohar@linux.ibm.com>]

On Tue, 2025-09-16 at 18:03 -0400, 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 <paul@paul-moore.com>

FYI, checkpatch.pl complains of unbalanced braces, otherwise

Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>

> ---
>  include/linux/lsm_hooks.h |  1 -
>  security/inode.c          | 43 ++++++++++++++++++++++++++++++++--
>  security/lsm_init.c       | 49 ---------------------------------------
>  3 files changed, 41 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..6620c3e42af2 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 || !len)) {
> +		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);
>  }
>  
>  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. */