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SubjectRe: [PATCH 09/10] LSM: Infrastructure management of the inode security
On Tue, Sep 11, 2018 at 9:42 AM, Casey Schaufler <casey@schaufler-ca.com> wrote:
> Move management of the inode->i_security blob out
> of the individual security modules and into the security
> infrastructure. Instead of allocating the blobs from within
> the modules the modules tell the infrastructure how much
> space is required, and the space is allocated there.
>
> Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
> ---
> include/linux/lsm_hooks.h | 3 ++
> security/security.c | 83 ++++++++++++++++++++++++++++++-
> security/selinux/hooks.c | 32 +-----------
> security/selinux/include/objsec.h | 5 +-
> security/smack/smack_lsm.c | 70 ++++----------------------
> 5 files changed, 98 insertions(+), 95 deletions(-)
>
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index 167ffbd4d0c0..416b20c3795b 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -2030,6 +2030,7 @@ struct security_hook_list {
> struct lsm_blob_sizes {
> int lbs_cred;
> int lbs_file;
> + int lbs_inode;
> };
>
> /*
> @@ -2092,9 +2093,11 @@ static inline void loadpin_add_hooks(void) { };
> #endif
>
> extern int lsm_cred_alloc(struct cred *cred, gfp_t gfp);
> +extern int lsm_inode_alloc(struct inode *inode);
>
> #ifdef CONFIG_SECURITY
> void lsm_early_cred(struct cred *cred);
> +void lsm_early_inode(struct inode *inode);
> #endif
>
> #endif /* ! __LINUX_LSM_HOOKS_H */
> diff --git a/security/security.c b/security/security.c
> index 5430cae73cf6..2501cdcbebff 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -41,6 +41,7 @@ struct security_hook_heads security_hook_heads __lsm_ro_after_init;
> static ATOMIC_NOTIFIER_HEAD(lsm_notifier_chain);
>
> static struct kmem_cache *lsm_file_cache;
> +static struct kmem_cache *lsm_inode_cache;
>
> char *lsm_names;
> static struct lsm_blob_sizes blob_sizes;
> @@ -101,6 +102,10 @@ int __init security_init(void)
> lsm_file_cache = kmem_cache_create("lsm_file_cache",
> blob_sizes.lbs_file, 0,
> SLAB_PANIC, NULL);
> + if (blob_sizes.lbs_inode)
> + lsm_inode_cache = kmem_cache_create("lsm_inode_cache",
> + blob_sizes.lbs_inode, 0,
> + SLAB_PANIC, NULL);
> /*
> * The second call to a module specific init function
> * adds hooks to the hook lists and does any other early
> @@ -111,6 +116,7 @@ int __init security_init(void)
> #ifdef CONFIG_SECURITY_LSM_DEBUG
> pr_info("LSM: cred blob size = %d\n", blob_sizes.lbs_cred);
> pr_info("LSM: file blob size = %d\n", blob_sizes.lbs_file);
> + pr_info("LSM: inode blob size = %d\n", blob_sizes.lbs_inode);
> #endif
>
> return 0;
> @@ -288,6 +294,13 @@ void __init security_add_blobs(struct lsm_blob_sizes *needed)
> {
> lsm_set_size(&needed->lbs_cred, &blob_sizes.lbs_cred);
> lsm_set_size(&needed->lbs_file, &blob_sizes.lbs_file);
> + /*
> + * The inode blob gets an rcu_head in addition to
> + * what the modules might need.
> + */
> + if (needed->lbs_inode && blob_sizes.lbs_inode == 0)
> + blob_sizes.lbs_inode = sizeof(struct rcu_head);
> + lsm_set_size(&needed->lbs_inode, &blob_sizes.lbs_inode);
> }
>
> /**
> @@ -311,6 +324,46 @@ int lsm_file_alloc(struct file *file)
> return 0;
> }
>
> +/**
> + * lsm_inode_alloc - allocate a composite inode blob
> + * @inode: the inode that needs a blob
> + *
> + * Allocate the inode blob for all the modules
> + *
> + * Returns 0, or -ENOMEM if memory can't be allocated.
> + */
> +int lsm_inode_alloc(struct inode *inode)
> +{
> + if (!lsm_inode_cache) {

WARN_ON?

> + inode->i_security = NULL;

The other patch didn't set to NULL. Probably should do that in the
other one too.

> + return 0;
> + }
> +
> + inode->i_security = kmem_cache_zalloc(lsm_inode_cache, GFP_NOFS);
> + if (inode->i_security == NULL)
> + return -ENOMEM;
> + return 0;
> +}
> +
> +/**
> + * lsm_early_inode - during initialization allocate a composite inode blob
> + * @inode: the inode that needs a blob
> + *
> + * Allocate the inode blob for all the modules if it's not already there
> + */
> +void lsm_early_inode(struct inode *inode)
> +{
> + int rc;
> +
> + if (inode == NULL)
> + panic("%s: NULL inode.\n", __func__);
> + if (inode->i_security != NULL)
> + return;
> + rc = lsm_inode_alloc(inode);
> + if (rc)
> + panic("%s: Early inode alloc failed.\n", __func__);
> +}

Same thoughts on the use of panic() as the other patch...

> +
> /*
> * Hook list operation macros.
> *
> @@ -557,14 +610,40 @@ EXPORT_SYMBOL(security_sb_parse_opts_str);
>
> int security_inode_alloc(struct inode *inode)
> {
> - inode->i_security = NULL;
> - return call_int_hook(inode_alloc_security, 0, inode);
> + int rc = lsm_inode_alloc(inode);
> +
> + if (unlikely(rc))
> + return rc;
> + rc = call_int_hook(inode_alloc_security, 0, inode);
> + if (unlikely(rc))
> + security_inode_free(inode);
> + return rc;
> +}
> +
> +static void inode_free_by_rcu(struct rcu_head *head)
> +{
> + /*
> + * The rcu head is at the start of the inode blob
> + */
> + kmem_cache_free(lsm_inode_cache, head);
> }
>
> void security_inode_free(struct inode *inode)
> {
> integrity_inode_free(inode);
> call_void_hook(inode_free_security, inode);
> + /*
> + * The inode may still be referenced in a path walk and
> + * a call to security_inode_permission() can be made
> + * after inode_free_security() is called. Ideally, the VFS
> + * wouldn't do this, but fixing that is a much harder
> + * job. For now, simply free the i_security via RCU, and
> + * leave the current inode->i_security pointer intact.
> + * The inode will be freed after the RCU grace period too.
> + */
> + if (inode->i_security)
> + call_rcu((struct rcu_head *)inode->i_security,
> + inode_free_by_rcu);
> }
>
> int security_dentry_init_security(struct dentry *dentry, int mode,
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 2720fe3ebf5f..0b593030d9f2 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -148,8 +148,6 @@ static int __init checkreqprot_setup(char *str)
> }
> __setup("checkreqprot=", checkreqprot_setup);
>
> -static struct kmem_cache *sel_inode_cache;
> -
> /**
> * selinux_secmark_enabled - Check to see if SECMARK is currently enabled
> *
> @@ -245,13 +243,9 @@ static inline u32 task_sid(const struct task_struct *task)
>
> static int inode_alloc_security(struct inode *inode)
> {
> - struct inode_security_struct *isec;
> + struct inode_security_struct *isec = selinux_inode(inode);
> u32 sid = current_sid();
>
> - isec = kmem_cache_zalloc(sel_inode_cache, GFP_NOFS);
> - if (!isec)
> - return -ENOMEM;
> -
> spin_lock_init(&isec->lock);
> INIT_LIST_HEAD(&isec->list);
> isec->inode = inode;
> @@ -259,7 +253,6 @@ static int inode_alloc_security(struct inode *inode)
> isec->sclass = SECCLASS_FILE;
> isec->task_sid = sid;
> isec->initialized = LABEL_INVALID;
> - inode->i_security = isec;
>
> return 0;
> }
> @@ -337,14 +330,6 @@ static struct inode_security_struct *backing_inode_security(struct dentry *dentr
> return selinux_inode(inode);
> }
>
> -static void inode_free_rcu(struct rcu_head *head)
> -{
> - struct inode_security_struct *isec;
> -
> - isec = container_of(head, struct inode_security_struct, rcu);
> - kmem_cache_free(sel_inode_cache, isec);
> -}
> -
> static void inode_free_security(struct inode *inode)
> {
> struct inode_security_struct *isec = selinux_inode(inode);
> @@ -365,17 +350,6 @@ static void inode_free_security(struct inode *inode)
> list_del_init(&isec->list);
> spin_unlock(&sbsec->isec_lock);
> }
> -
> - /*
> - * The inode may still be referenced in a path walk and
> - * a call to selinux_inode_permission() can be made
> - * after inode_free_security() is called. Ideally, the VFS
> - * wouldn't do this, but fixing that is a much harder
> - * job. For now, simply free the i_security via RCU, and
> - * leave the current inode->i_security pointer intact.
> - * The inode will be freed after the RCU grace period too.
> - */
> - call_rcu(&isec->rcu, inode_free_rcu);
> }
>
> static int file_alloc_security(struct file *file)
> @@ -6840,6 +6814,7 @@ static void selinux_bpf_prog_free(struct bpf_prog_aux *aux)
> struct lsm_blob_sizes selinux_blob_sizes = {
> .lbs_cred = sizeof(struct task_security_struct),
> .lbs_file = sizeof(struct file_security_struct),
> + .lbs_inode = sizeof(struct inode_security_struct),
> };
>
> static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
> @@ -7109,9 +7084,6 @@ static __init int selinux_init(void)
>
> default_noexec = !(VM_DATA_DEFAULT_FLAGS & VM_EXEC);
>
> - sel_inode_cache = kmem_cache_create("selinux_inode_security",
> - sizeof(struct inode_security_struct),
> - 0, SLAB_PANIC, NULL);
> avc_init();
>
> avtab_cache_init();
> diff --git a/security/selinux/include/objsec.h b/security/selinux/include/objsec.h
> index 3304a1ee58a4..7a3d18fa9b13 100644
> --- a/security/selinux/include/objsec.h
> +++ b/security/selinux/include/objsec.h
> @@ -59,10 +59,7 @@ enum label_initialized {
>
> struct inode_security_struct {
> struct inode *inode; /* back pointer to inode object */
> - union {
> - struct list_head list; /* list of inode_security_struct */
> - struct rcu_head rcu; /* for freeing the inode_security_struct */
> - };
> + struct list_head list; /* list of inode_security_struct */
> u32 task_sid; /* SID of creating task */
> u32 sid; /* SID of this object */
> u16 sclass; /* security class of this object */
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index 364699ad55b9..6617abb51732 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -288,24 +288,18 @@ static struct smack_known *smk_fetch(const char *name, struct inode *ip,
> }
>
> /**
> - * new_inode_smack - allocate an inode security blob
> + * init_inode_smack - initialize an inode security blob
> + * @isp: the blob to initialize
> * @skp: a pointer to the Smack label entry to use in the blob
> *
> - * Returns the new blob or NULL if there's no memory available
> */
> -static struct inode_smack *new_inode_smack(struct smack_known *skp)
> +static void init_inode_smack(struct inode *inode, struct smack_known *skp)
> {
> - struct inode_smack *isp;
> -
> - isp = kmem_cache_zalloc(smack_inode_cache, GFP_NOFS);
> - if (isp == NULL)
> - return NULL;
> + struct inode_smack *isp = smack_inode(inode);
>
> isp->smk_inode = skp;
> isp->smk_flags = 0;
> mutex_init(&isp->smk_lock);
> -
> - return isp;
> }
>
> /**
> @@ -824,17 +818,13 @@ static int smack_set_mnt_opts(struct super_block *sb,
> /*
> * Initialize the root inode.
> */
> - isp = smack_inode(inode);
> - if (isp == NULL) {
> - isp = new_inode_smack(sp->smk_root);
> - if (isp == NULL)
> - return -ENOMEM;
> - inode->i_security = isp;
> - } else
> - isp->smk_inode = sp->smk_root;
> + lsm_early_inode(inode);
> + init_inode_smack(inode, sp->smk_root);
>
> - if (transmute)
> + if (transmute) {
> + isp = smack_inode(inode);
> isp->smk_flags |= SMK_INODE_TRANSMUTE;
> + }
>
> return 0;
> }
> @@ -963,48 +953,10 @@ static int smack_inode_alloc_security(struct inode *inode)
> {
> struct smack_known *skp = smk_of_current();
>
> - inode->i_security = new_inode_smack(skp);
> - if (inode->i_security == NULL)
> - return -ENOMEM;
> + init_inode_smack(inode, skp);
> return 0;
> }
>
> -/**
> - * smack_inode_free_rcu - Free inode_smack blob from cache
> - * @head: the rcu_head for getting inode_smack pointer
> - *
> - * Call back function called from call_rcu() to free
> - * the i_security blob pointer in inode
> - */
> -static void smack_inode_free_rcu(struct rcu_head *head)
> -{
> - struct inode_smack *issp;
> -
> - issp = container_of(head, struct inode_smack, smk_rcu);
> - kmem_cache_free(smack_inode_cache, issp);
> -}
> -
> -/**
> - * smack_inode_free_security - free an inode blob using call_rcu()
> - * @inode: the inode with a blob
> - *
> - * Clears the blob pointer in inode using RCU
> - */
> -static void smack_inode_free_security(struct inode *inode)
> -{
> - struct inode_smack *issp = smack_inode(inode);
> -
> - /*
> - * The inode may still be referenced in a path walk and
> - * a call to smack_inode_permission() can be made
> - * after smack_inode_free_security() is called.
> - * To avoid race condition free the i_security via RCU
> - * and leave the current inode->i_security pointer intact.
> - * The inode will be freed after the RCU grace period too.
> - */
> - call_rcu(&issp->smk_rcu, smack_inode_free_rcu);
> -}
> -
> /**
> * smack_inode_init_security - copy out the smack from an inode
> * @inode: the newly created inode
> @@ -4619,6 +4571,7 @@ static int smack_dentry_create_files_as(struct dentry *dentry, int mode,
> struct lsm_blob_sizes smack_blob_sizes = {
> .lbs_cred = sizeof(struct task_smack),
> .lbs_file = sizeof(struct smack_known *),
> + .lbs_inode = sizeof(struct inode_smack),
> };
>
> static struct security_hook_list smack_hooks[] __lsm_ro_after_init = {
> @@ -4637,7 +4590,6 @@ static struct security_hook_list smack_hooks[] __lsm_ro_after_init = {
> LSM_HOOK_INIT(bprm_set_creds, smack_bprm_set_creds),
>
> LSM_HOOK_INIT(inode_alloc_security, smack_inode_alloc_security),
> - LSM_HOOK_INIT(inode_free_security, smack_inode_free_security),
> LSM_HOOK_INIT(inode_init_security, smack_inode_init_security),
> LSM_HOOK_INIT(inode_link, smack_inode_link),
> LSM_HOOK_INIT(inode_unlink, smack_inode_unlink),
> --
> 2.17.1
>
>

I continue to really like this series: I think pulling the memory
management up into the core LSM makes things much cleaner.

-Kees

--
Kees Cook
Pixel Security

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