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Message-ID: <ea813695-ef75-4244-8855-d739303f17f6@huaweicloud.com>
Date: Wed, 15 Jan 2025 11:45:22 +0100
From: Roberto Sassu <roberto.sassu@...weicloud.com>
To: Mimi Zohar <zohar@...ux.ibm.com>, viro@...iv.linux.org.uk,
brauner@...nel.org, jack@...e.cz, dmitry.kasatkin@...il.com,
eric.snowberg@...cle.com, paul@...l-moore.com, jmorris@...ei.org,
serge@...lyn.com
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-integrity@...r.kernel.org, linux-security-module@...r.kernel.org,
Roberto Sassu <roberto.sassu@...wei.com>
Subject: Re: [PATCH v2 2/7] ima: Remove inode lock
On 1/14/2025 2:35 PM, Mimi Zohar wrote:
> On Thu, 2024-11-28 at 11:06 +0100, Roberto Sassu wrote:
>> From: Roberto Sassu <roberto.sassu@...wei.com>
>>
>> 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@...wei.com>
>> Reviewed-by: Paul Moore <paul@...l-moore.com>
>> ---
>> 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?
Yes, ima_inode_free_rcu() only provides the inode security blob, and not
the inode itself.
Thanks
Roberto
> 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) = {
>
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