ima: add the ability to query the cached hash of a given file

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

Florent Revest committed 6 years ago

Commit 6beea7a1 parent 5350ceb2 files · +55 −0Browse files

Unified · Split

2 files

include/linux/ima.h +6 −0
security/integrity/ima/ima_main.c +49 −0

include/linux/ima.h+6−0

 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
 	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 */

security/integrity/ima/ima_main.c+49−0

@@ -445,6 +445,55 @@ int ima_file_check(struct file *file, int mask) · 444 unmodified lines
445	}	445	}
446	EXPORT_SYMBOL_GPL(ima_file_check);	446	EXPORT_SYMBOL_GPL(ima_file_check);
447		447
		448	/**
		449	* ima_file_hash - return the stored measurement if a file has been hashed and
		450	* is in the iint cache.
		451	* @file: pointer to the file
		452	* @buf: buffer in which to store the hash
		453	* @buf_size: length of the buffer
		454	*
		455	* On success, return the hash algorithm (as defined in the enum hash_algo).
		456	* If buf is not NULL, this function also outputs the hash into buf.
		457	* If the hash is larger than buf_size, then only buf_size bytes will be copied.
		458	* It generally just makes sense to pass a buffer capable of holding the largest
		459	* possible hash: IMA_MAX_DIGEST_SIZE.
		460	* The file hash returned is based on the entire file, including the appended
		461	* signature.
		462	*
		463	* If IMA is disabled or if no measurement is available, return -EOPNOTSUPP.
		464	* If the parameters are incorrect, return -EINVAL.
		465	*/
		466	int ima_file_hash(struct file file, char buf, size_t buf_size)
		467	{
		468	struct inode *inode;
		469	struct integrity_iint_cache *iint;
		470	int hash_algo;
		471
		472	if (!file)
		473	return -EINVAL;
		474
		475	if (!ima_policy_flag)
		476	return -EOPNOTSUPP;
		477
		478	inode = file_inode(file);
		479	iint = integrity_iint_find(inode);
		480	if (!iint)
		481	return -EOPNOTSUPP;
		482
		483	mutex_lock(&iint->mutex);
		484	if (buf) {
		485	size_t copied_size;
		486
		487	copied_size = min_t(size_t, iint->ima_hash->length, buf_size);
		488	memcpy(buf, iint->ima_hash->digest, copied_size);
		489	}
		490	hash_algo = iint->ima_hash->algo;
		491	mutex_unlock(&iint->mutex);
		492
		493	return hash_algo;
		494	}
		495	EXPORT_SYMBOL_GPL(ima_file_hash);
		496
448	/**	497	/**
449	* ima_post_create_tmpfile - mark newly created tmpfile as new	498	* ima_post_create_tmpfile - mark newly created tmpfile as new
450	* @file : newly created tmpfile	499	* @file : newly created tmpfile