From: Florent Revest <revest@xxxxxxxxxx> This allows other parts of the kernel (perhaps a stacked LSM allowing system monitoring, eg. the proposed KRSI LSM [1]) to retrieve the hash of a given file from IMA if it's present in the iint cache. It's true that the existence of the hash means that it's also in the audit logs or in /sys/kernel/security/ima/ascii_runtime_measurements, but it can be difficult to pull that information out for every subsequent exec. This is especially true if a given host has been up for a long time and the file was first measured a long time ago. It should be kept in mind that this function gives access to cached entries which can be removed, for instance on security_inode_free(). This is based on Peter Moody's patch: https://sourceforge.net/p/linux-ima/mailman/message/33036180/ [1] https://lkml.org/lkml/2019/9/10/393 Signed-off-by: Florent Revest <revest@xxxxxxxxxx> --- include/linux/ima.h | 6 ++++ security/integrity/ima/ima_main.c | 49 +++++++++++++++++++++++++++++++ 2 files changed, 55 insertions(+) diff --git a/include/linux/ima.h b/include/linux/ima.h index f4644c54f648..1659217e9b60 100644 --- a/include/linux/ima.h +++ b/include/linux/ima.h @@ -23,6 +23,7 @@ extern int ima_read_file(struct file *file, enum kernel_read_file_id id); extern int ima_post_read_file(struct file *file, void *buf, loff_t size, enum kernel_read_file_id id); extern void ima_post_path_mknod(struct dentry *dentry); +extern int ima_file_hash(struct file *file, char *buf, size_t buf_size); extern void ima_kexec_cmdline(const void *buf, int size); #ifdef CONFIG_IMA_KEXEC @@ -91,6 +92,11 @@ static inline void ima_post_path_mknod(struct dentry *dentry) return; } +static inline int ima_file_hash(struct file *file, char *buf, size_t buf_size) +{ + return -EOPNOTSUPP; +} + static inline void ima_kexec_cmdline(const void *buf, int size) {} #endif /* CONFIG_IMA */ diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c index 2272c3255c7d..9fe949c6a530 100644 --- a/security/integrity/ima/ima_main.c +++ b/security/integrity/ima/ima_main.c @@ -445,6 +445,55 @@ int ima_file_check(struct file *file, int mask) } EXPORT_SYMBOL_GPL(ima_file_check); +/** + * ima_file_hash - return the stored measurement if a file has been hashed and + * is in the iint cache. + * @file: pointer to the file + * @buf: buffer in which to store the hash + * @buf_size: length of the buffer + * + * On success, return the hash algorithm (as defined in the enum hash_algo). + * If buf is not NULL, this function also outputs the hash into buf. + * If the hash is larger than buf_size, then only buf_size bytes will be copied. + * It generally just makes sense to pass a buffer capable of holding the largest + * possible hash: IMA_MAX_DIGEST_SIZE. + * The file hash returned is based on the entire file, including the appended + * signature. + * + * If IMA is disabled or if no measurement is available, return -EOPNOTSUPP. + * If the parameters are incorrect, return -EINVAL. + */ +int ima_file_hash(struct file *file, char *buf, size_t buf_size) +{ + struct inode *inode; + struct integrity_iint_cache *iint; + int hash_algo; + + if (!file) + return -EINVAL; + + if (!ima_policy_flag) + return -EOPNOTSUPP; + + inode = file_inode(file); + iint = integrity_iint_find(inode); + if (!iint) + return -EOPNOTSUPP; + + mutex_lock(&iint->mutex); + if (buf) { + size_t copied_size; + + copied_size = min_t(size_t, iint->ima_hash->length, buf_size); + memcpy(buf, iint->ima_hash->digest, copied_size); + } + hash_algo = iint->ima_hash->algo; + mutex_unlock(&iint->mutex); + + return hash_algo; +} +EXPORT_SYMBOL_GPL(ima_file_hash); + /** * ima_post_create_tmpfile - mark newly created tmpfile as new * @file : newly created tmpfile -- 2.25.0.rc1.283.g88dfdc4193-goog
