Commit 403319be authored by KP Singh's avatar KP Singh Committed by Daniel Borkmann
Browse files

ima: Implement ima_inode_hash 



This is in preparation to add a helper for BPF LSM programs to use
IMA hashes when attached to LSM hooks. There are LSM hooks like
inode_unlink which do not have a struct file * argument and cannot
use the existing ima_file_hash API.

An inode based API is, therefore, useful in LSM based detections like an
executable trying to delete itself which rely on the inode_unlink LSM
hook.

Moreover, the ima_file_hash function does nothing with the struct file
pointer apart from calling file_inode on it and converting it to an
inode.

Signed-off-by: default avatarKP Singh <kpsingh@google.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarYonghong Song <yhs@fb.com>
Acked-by: default avatarMimi Zohar <zohar@linux.ibm.com>
Link: https://lore.kernel.org/bpf/20201124151210.1081188-2-kpsingh@chromium.org
parent db13db9f

include/linux/ima.h

+6 −0
Original line number Diff line number Diff line
@@ -29,6 +29,7 @@ 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 int ima_inode_hash(struct inode *inode, char *buf, size_t buf_size);

extern void ima_kexec_cmdline(int kernel_fd, const void *buf, int size);



#ifdef CONFIG_IMA_KEXEC
@@ -115,6 +116,11 @@ static inline int ima_file_hash(struct file *file, char *buf, size_t buf_size) 
	return -EOPNOTSUPP;

}



static inline int ima_inode_hash(struct inode *inode, char *buf, size_t buf_size)

{

	return -EOPNOTSUPP;

}



static inline void ima_kexec_cmdline(int kernel_fd, const void *buf, int size) {}

#endif /* CONFIG_IMA */

security/integrity/ima/ima_main.c

+54 −24
Original line number Diff line number Diff line
@@ -501,37 +501,14 @@ 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)

static int __ima_inode_hash(struct inode *inode, 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;
@@ -558,8 +535,61 @@ int ima_file_hash(struct file *file, char *buf, size_t buf_size) 


	return hash_algo;

}



/**

 * 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)

{

	if (!file)

		return -EINVAL;



	return __ima_inode_hash(file_inode(file), buf, buf_size);

}

EXPORT_SYMBOL_GPL(ima_file_hash);



/**

 * ima_inode_hash - return the stored measurement if the inode has been hashed

 * and is in the iint cache.

 * @inode: pointer to the inode

 * @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 hash returned is based on the entire contents, 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_inode_hash(struct inode *inode, char *buf, size_t buf_size)

{

	if (!inode)

		return -EINVAL;



	return __ima_inode_hash(inode, buf, buf_size);

}

EXPORT_SYMBOL_GPL(ima_inode_hash);



/**

 * ima_post_create_tmpfile - mark newly created tmpfile as new

 * @file : newly created tmpfile

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