On 4/9/2025 11:49 AM, 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 an as-needed basis when
> userspace reads "/sys/kernel/security/lsm".
>
> Signed-off-by: Paul Moore <p...@paul-moore.com>
> ---
> include/linux/lsm_hooks.h | 1 -
> security/inode.c | 27 +++++++++++++++++++--
> security/lsm_init.c | 49 ---------------------------------------
> 3 files changed, 25 insertions(+), 52 deletions(-)
>
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index 4cd17c9a229f..bc477fb20d02 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -169,7 +169,6 @@ 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 da3ab44c8e57..49bc3578bd23 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;
>
> @@ -343,8 +345,29 @@ 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;
> + char *str;
> + ssize_t rc, len = 0;
> +
> + for (i = 0; i < lsm_count; i++)
> + /* the '+ 1' accounts for either a comma or a NUL terminator */
> + len += strlen(lsm_order[i]->id->name) + 1;
> +
> + str = kmalloc(len, GFP_KERNEL);
> + if (!str)
> + return -ENOMEM;
> + str[0] = '\0';
> +
> + i = 0;
> + while (i < lsm_count) {
> + strcat(str, lsm_order[i]->id->name);
> + if (++i < lsm_count)
> + strcat(str, ",");
> + }
> +
> + rc = simple_read_from_buffer(buf, count, ppos, str, len);
This results in a trailing nul byte at the end of the string.
> + kfree(str);
> + return rc;
> }
>
> static const struct file_operations lsm_ops = {
> diff --git a/security/lsm_init.c b/security/lsm_init.c
> index 981ddb20f48e..978bb81b58fa 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[];
> @@ -363,42 +361,6 @@ 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;
> @@ -435,15 +397,6 @@ 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)
> @@ -480,8 +433,6 @@ 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. */
