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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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 > --- > 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 > #include > > +#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 > + > 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. */