Commit 6beea7af authored by Florent Revest's avatar Florent Revest Committed by Mimi Zohar
Browse files

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



Signed-off-by: default avatarFlorent Revest <revest@google.com>
Reviewed-by: default avatarKP Singh <kpsingh@chromium.org>
Signed-off-by: default avatarMimi Zohar <zohar@linux.ibm.com>
parent 5350ceb0

include/linux/ima.h

+6 −0
Original line number Diff line number Diff line
@@ -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 */

security/integrity/ima/ima_main.c

+49 −0
Original line number Diff line number Diff line
@@ -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

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