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

@@ -23,6 +23,7 @@ extern int ima_read_file(struct file *file, enum kernel_read_file_id id); · 22 unmodified lines
23	23	extern int ima_post_read_file(struct file file, void buf, loff_t size,
24	24	enum kernel_read_file_id id);
25	25	extern void ima_post_path_mknod(struct dentry *dentry);
	26	+extern int ima_file_hash(struct file file, char buf, size_t buf_size);
26	27	extern void ima_kexec_cmdline(const void *buf, int size);
27	28
28	29	#ifdef CONFIG_IMA_KEXEC
@@ -91,6 +92,11 @@ static inline void ima_post_path_mknod(struct dentry *dentry) · 62 unmodified lines
91	92	return;
92	93	}
93	94
	95	+static inline int ima_file_hash(struct file file, char buf, size_t buf_size)
	96	+{
	97	+ return -EOPNOTSUPP;
	98	+}
	99	+
94	100	static inline void ima_kexec_cmdline(const void *buf, int size) {}
95	101	#endif /* CONFIG_IMA */
96	102

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	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	498	* ima_post_create_tmpfile - mark newly created tmpfile as new
450	499	* @file : newly created tmpfile