Re: [PATCH v2 2/7] ima: Remove inode lock
From: Mimi Zohar
Date: Tue Jan 14 2025 - 08:36:33 EST
On Thu, 2024-11-28 at 11:06 +0100, Roberto Sassu wrote:
> From: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
>
> Move out the mutex in the ima_iint_cache structure to a new structure
> called ima_iint_cache_lock, so that a lock can be taken regardless of
> whether or not inode integrity metadata are stored in the inode.
>
> Introduce ima_inode_security() to retrieve the ima_iint_cache_lock
> structure, if inode i_security is not NULL, and consequently remove
> ima_inode_get_iint() and ima_inode_set_iint(), since the ima_iint_cache
> structure can be read and modified from the new structure.
>
> Move the mutex initialization and annotation in the new function
> ima_inode_alloc_security() and introduce ima_iint_lock() and
> ima_iint_unlock() to respectively lock and unlock the mutex.
>
> Finally, expand the critical region in process_measurement() guarded by
> iint->mutex up to where the inode was locked, use only one iint lock in
> __ima_inode_hash(), since the mutex is now in the inode security blob, and
> replace the inode_lock()/inode_unlock() calls in ima_check_last_writer().
>
> Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> Reviewed-by: Paul Moore <paul@xxxxxxxxxxxxxx>
> ---
> security/integrity/ima/ima.h | 31 ++++-------
> security/integrity/ima/ima_api.c | 4 +-
> security/integrity/ima/ima_iint.c | 92 ++++++++++++++++++++++++++-----
> security/integrity/ima/ima_main.c | 39 ++++++-------
> 4 files changed, 109 insertions(+), 57 deletions(-)
>
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index 3f1a82b7cd71..b4eeab48f08a 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -182,7 +182,6 @@ struct ima_kexec_hdr {
>
> /* IMA integrity metadata associated with an inode */
> struct ima_iint_cache {
> - struct mutex mutex; /* protects: version, flags, digest */
> struct integrity_inode_attributes real_inode;
> unsigned long flags;
> unsigned long measured_pcrs;
> @@ -195,35 +194,27 @@ struct ima_iint_cache {
> struct ima_digest_data *ima_hash;
> };
>
> +struct ima_iint_cache_lock {
> + struct mutex mutex; /* protects: iint version, flags, digest */
> + struct ima_iint_cache *iint;
> +};
> +
> extern struct lsm_blob_sizes ima_blob_sizes;
>
> -static inline struct ima_iint_cache *
> -ima_inode_get_iint(const struct inode *inode)
> +static inline struct ima_iint_cache_lock *ima_inode_security(void *i_security)
> {
Is there a reason for naming the function ima_inode_security() and passing
i_security, when the other LSMs name it <lsm>_inode() and pass the inode?
static inline struct inode_smack *smack_inode(const struct inode *inode)
static inline struct inode_security_struct *selinux_inode(const struct inode *inode)
static inline struct landlock_inode_security *landlock_inode(const struct inode
*const inode)
Mimi
> - struct ima_iint_cache **iint_sec;
> -
> - if (unlikely(!inode->i_security))
> + if (unlikely(!i_security))
> return NULL;
>
> - iint_sec = inode->i_security + ima_blob_sizes.lbs_inode;
> - return *iint_sec;
> -}
> -
> -static inline void ima_inode_set_iint(const struct inode *inode,
> - struct ima_iint_cache *iint)
> -{
> - struct ima_iint_cache **iint_sec;
> -
> - if (unlikely(!inode->i_security))
> - return;
> -
> - iint_sec = inode->i_security + ima_blob_sizes.lbs_inode;
> - *iint_sec = iint;
> + return i_security + ima_blob_sizes.lbs_inode;
> }
>
> struct ima_iint_cache *ima_iint_find(struct inode *inode);
> struct ima_iint_cache *ima_inode_get(struct inode *inode);
> +int ima_inode_alloc_security(struct inode *inode);
> void ima_inode_free_rcu(void *inode_security);
> +void ima_iint_lock(struct inode *inode);
> +void ima_iint_unlock(struct inode *inode);
> void __init ima_iintcache_init(void);
>
> extern const int read_idmap[];
> diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
> index 984e861f6e33..37c2a228f0e1 100644
> --- a/security/integrity/ima/ima_api.c
> +++ b/security/integrity/ima/ima_api.c
> @@ -234,7 +234,7 @@ static bool ima_get_verity_digest(struct ima_iint_cache *iint,
> * Calculate the file hash, if it doesn't already exist,
> * storing the measurement and i_version in the iint.
> *
> - * Must be called with iint->mutex held.
> + * Must be called with iint mutex held.
> *
> * Return 0 on success, error code otherwise
> */
> @@ -343,7 +343,7 @@ int ima_collect_measurement(struct ima_iint_cache *iint, struct
> file *file,
> * - the inode was previously flushed as well as the iint info,
> * containing the hashing info.
> *
> - * Must be called with iint->mutex held.
> + * Must be called with iint mutex held.
> */
> void ima_store_measurement(struct ima_iint_cache *iint, struct file *file,
> const unsigned char *filename,
> diff --git a/security/integrity/ima/ima_iint.c b/security/integrity/ima/ima_iint.c
> index 9d9fc7a911ad..dcc32483d29f 100644
> --- a/security/integrity/ima/ima_iint.c
> +++ b/security/integrity/ima/ima_iint.c
> @@ -26,7 +26,13 @@ static struct kmem_cache *ima_iint_cache __ro_after_init;
> */
> struct ima_iint_cache *ima_iint_find(struct inode *inode)
> {
> - return ima_inode_get_iint(inode);
> + struct ima_iint_cache_lock *iint_lock;
> +
> + iint_lock = ima_inode_security(inode->i_security);
> + if (!iint_lock)
> + return NULL;
> +
> + return iint_lock->iint;
> }
>
> #define IMA_MAX_NESTING (FILESYSTEM_MAX_STACK_DEPTH + 1)
> @@ -37,18 +43,18 @@ struct ima_iint_cache *ima_iint_find(struct inode *inode)
> * mutex to avoid lockdep false positives related to IMA + overlayfs.
> * See ovl_lockdep_annotate_inode_mutex_key() for more details.
> */
> -static inline void ima_iint_lockdep_annotate(struct ima_iint_cache *iint,
> - struct inode *inode)
> +static inline void ima_iint_lock_lockdep_annotate(struct mutex *mutex,
> + struct inode *inode)
> {
> #ifdef CONFIG_LOCKDEP
> - static struct lock_class_key ima_iint_mutex_key[IMA_MAX_NESTING];
> + static struct lock_class_key ima_iint_lock_mutex_key[IMA_MAX_NESTING];
>
> int depth = inode->i_sb->s_stack_depth;
>
> if (WARN_ON_ONCE(depth < 0 || depth >= IMA_MAX_NESTING))
> depth = 0;
>
> - lockdep_set_class(&iint->mutex, &ima_iint_mutex_key[depth]);
> + lockdep_set_class(mutex, &ima_iint_lock_mutex_key[depth]);
> #endif
> }
>
> @@ -65,14 +71,11 @@ static void ima_iint_init_always(struct ima_iint_cache *iint,
> iint->ima_read_status = INTEGRITY_UNKNOWN;
> iint->ima_creds_status = INTEGRITY_UNKNOWN;
> iint->measured_pcrs = 0;
> - mutex_init(&iint->mutex);
> - ima_iint_lockdep_annotate(iint, inode);
> }
>
> static void ima_iint_free(struct ima_iint_cache *iint)
> {
> kfree(iint->ima_hash);
> - mutex_destroy(&iint->mutex);
> kmem_cache_free(ima_iint_cache, iint);
> }
>
> @@ -87,9 +90,14 @@ static void ima_iint_free(struct ima_iint_cache *iint)
> */
> struct ima_iint_cache *ima_inode_get(struct inode *inode)
> {
> + struct ima_iint_cache_lock *iint_lock;
> struct ima_iint_cache *iint;
>
> - iint = ima_iint_find(inode);
> + iint_lock = ima_inode_security(inode->i_security);
> + if (!iint_lock)
> + return NULL;
> +
> + iint = iint_lock->iint;
> if (iint)
> return iint;
>
> @@ -99,11 +107,31 @@ struct ima_iint_cache *ima_inode_get(struct inode *inode)
>
> ima_iint_init_always(iint, inode);
>
> - ima_inode_set_iint(inode, iint);
> + iint_lock->iint = iint;
>
> return iint;
> }
>
> +/**
> + * ima_inode_alloc_security - Called to init an inode
> + * @inode: Pointer to the inode
> + *
> + * Initialize and annotate the mutex in the ima_iint_cache_lock structure.
> + *
> + * Return: Zero.
> + */
> +int ima_inode_alloc_security(struct inode *inode)
> +{
> + struct ima_iint_cache_lock *iint_lock;
> +
> + iint_lock = ima_inode_security(inode->i_security);
> +
> + mutex_init(&iint_lock->mutex);
> + ima_iint_lock_lockdep_annotate(&iint_lock->mutex, inode);
> +
> + return 0;
> +}
> +
> /**
> * ima_inode_free_rcu - Called to free an inode via a RCU callback
> * @inode_security: The inode->i_security pointer
> @@ -112,10 +140,48 @@ struct ima_iint_cache *ima_inode_get(struct inode *inode)
> */
> void ima_inode_free_rcu(void *inode_security)
> {
> - struct ima_iint_cache **iint_p = inode_security +
> ima_blob_sizes.lbs_inode;
> + struct ima_iint_cache_lock *iint_lock;
> +
> + iint_lock = ima_inode_security(inode_security);
> +
> + mutex_destroy(&iint_lock->mutex);
> +
> + if (iint_lock->iint)
> + ima_iint_free(iint_lock->iint);
> +}
> +
> +/**
> + * ima_iint_lock - Lock integrity metadata
> + * @inode: Pointer to the inode
> + *
> + * Lock integrity metadata.
> + */
> +void ima_iint_lock(struct inode *inode)
> +{
> + struct ima_iint_cache_lock *iint_lock;
> +
> + iint_lock = ima_inode_security(inode->i_security);
> +
> + /* Only inodes with i_security are processed by IMA. */
> + if (iint_lock)
> + mutex_lock(&iint_lock->mutex);
> +}
> +
> +/**
> + * ima_iint_unlock - Unlock integrity metadata
> + * @inode: Pointer to the inode
> + *
> + * Unlock integrity metadata.
> + */
> +void ima_iint_unlock(struct inode *inode)
> +{
> + struct ima_iint_cache_lock *iint_lock;
> +
> + iint_lock = ima_inode_security(inode->i_security);
>
> - if (*iint_p)
> - ima_iint_free(*iint_p);
> + /* Only inodes with i_security are processed by IMA. */
> + if (iint_lock)
> + mutex_unlock(&iint_lock->mutex);
> }
>
> static void ima_iint_init_once(void *foo)
> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> index cea0afbbc28d..05cfb04cd02b 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -163,7 +163,7 @@ static void ima_check_last_writer(struct ima_iint_cache *iint,
> if (!(mode & FMODE_WRITE))
> return;
>
> - mutex_lock(&iint->mutex);
> + ima_iint_lock(inode);
> if (atomic_read(&inode->i_writecount) == 1) {
> struct kstat stat;
>
> @@ -181,7 +181,7 @@ static void ima_check_last_writer(struct ima_iint_cache *iint,
> ima_update_xattr(iint, file);
> }
> }
> - mutex_unlock(&iint->mutex);
> + ima_iint_unlock(inode);
> }
>
> /**
> @@ -247,7 +247,7 @@ static int process_measurement(struct file *file, const struct
> cred *cred,
> if (action & IMA_FILE_APPRAISE)
> func = FILE_CHECK;
>
> - inode_lock(inode);
> + ima_iint_lock(inode);
>
> if (action) {
> iint = ima_inode_get(inode);
> @@ -259,15 +259,11 @@ static int process_measurement(struct file *file, const
> struct cred *cred,
> ima_rdwr_violation_check(file, iint, action & IMA_MEASURE,
> &pathbuf, &pathname, filename);
>
> - inode_unlock(inode);
> -
> if (rc)
> goto out;
> if (!action)
> goto out;
>
> - mutex_lock(&iint->mutex);
> -
> if (test_and_clear_bit(IMA_CHANGE_ATTR, &iint->atomic_flags))
> /* reset appraisal flags if ima_inode_post_setattr was called */
> iint->flags &= ~(IMA_APPRAISE | IMA_APPRAISED |
> @@ -412,10 +408,10 @@ static int process_measurement(struct file *file, const
> struct cred *cred,
> if ((mask & MAY_WRITE) && test_bit(IMA_DIGSIG, &iint->atomic_flags) &&
> !(iint->flags & IMA_NEW_FILE))
> rc = -EACCES;
> - mutex_unlock(&iint->mutex);
> kfree(xattr_value);
> ima_free_modsig(modsig);
> out:
> + ima_iint_unlock(inode);
> if (pathbuf)
> __putname(pathbuf);
> if (must_appraise) {
> @@ -580,18 +576,13 @@ static int __ima_inode_hash(struct inode *inode, struct file
> *file, char *buf,
> struct ima_iint_cache *iint = NULL, tmp_iint;
> int rc, hash_algo;
>
> - if (ima_policy_flag) {
> + ima_iint_lock(inode);
> +
> + if (ima_policy_flag)
> iint = ima_iint_find(inode);
> - if (iint)
> - mutex_lock(&iint->mutex);
> - }
>
> if ((!iint || !(iint->flags & IMA_COLLECTED)) && file) {
> - if (iint)
> - mutex_unlock(&iint->mutex);
> -
> memset(&tmp_iint, 0, sizeof(tmp_iint));
> - mutex_init(&tmp_iint.mutex);
>
> rc = ima_collect_measurement(&tmp_iint, file, NULL, 0,
> ima_hash_algo, NULL);
> @@ -600,22 +591,24 @@ static int __ima_inode_hash(struct inode *inode, struct file
> *file, char *buf,
> if (rc != -ENOMEM)
> kfree(tmp_iint.ima_hash);
>
> + ima_iint_unlock(inode);
> return -EOPNOTSUPP;
> }
>
> iint = &tmp_iint;
> - mutex_lock(&iint->mutex);
> }
>
> - if (!iint)
> + if (!iint) {
> + ima_iint_unlock(inode);
> return -EOPNOTSUPP;
> + }
>
> /*
> * ima_file_hash can be called when ima_collect_measurement has still
> * not been called, we might not always have a hash.
> */
> if (!iint->ima_hash || !(iint->flags & IMA_COLLECTED)) {
> - mutex_unlock(&iint->mutex);
> + ima_iint_unlock(inode);
> return -EOPNOTSUPP;
> }
>
> @@ -626,11 +619,12 @@ static int __ima_inode_hash(struct inode *inode, struct file
> *file, char *buf,
> memcpy(buf, iint->ima_hash->digest, copied_size);
> }
> hash_algo = iint->ima_hash->algo;
> - mutex_unlock(&iint->mutex);
>
> if (iint == &tmp_iint)
> kfree(iint->ima_hash);
>
> + ima_iint_unlock(inode);
> +
> return hash_algo;
> }
>
> @@ -1118,7 +1112,7 @@ EXPORT_SYMBOL_GPL(ima_measure_critical_data);
> * @kmod_name: kernel module name
> *
> * Avoid a verification loop where verifying the signature of the modprobe
> - * binary requires executing modprobe itself. Since the modprobe iint->mutex
> + * binary requires executing modprobe itself. Since the modprobe iint mutex
> * is already held when the signature verification is performed, a deadlock
> * occurs as soon as modprobe is executed within the critical region, since
> * the same lock cannot be taken again.
> @@ -1193,6 +1187,7 @@ static struct security_hook_list ima_hooks[] __ro_after_init
> = {
> #ifdef CONFIG_INTEGRITY_ASYMMETRIC_KEYS
> LSM_HOOK_INIT(kernel_module_request, ima_kernel_module_request),
> #endif
> + LSM_HOOK_INIT(inode_alloc_security, ima_inode_alloc_security),
> LSM_HOOK_INIT(inode_free_security_rcu, ima_inode_free_rcu),
> };
>
> @@ -1210,7 +1205,7 @@ static int __init init_ima_lsm(void)
> }
>
> struct lsm_blob_sizes ima_blob_sizes __ro_after_init = {
> - .lbs_inode = sizeof(struct ima_iint_cache *),
> + .lbs_inode = sizeof(struct ima_iint_cache_lock),
> };
>
> DEFINE_LSM(ima) = {