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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: KP Singh <kpsingh@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: Mimi Zohar <zohar@linux.ibm.com>
Link: https://lore.kernel.org/bpf/20201124151210.1081188-2-kpsingh@chromium.org
zero-sugar-mainline-defconfig
KP Singh 2020-11-24 15:12:08 +00:00 committed by Daniel Borkmann
parent db13db9f67
commit 403319be5d
2 changed files with 60 additions and 24 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
include/linux/ima.h
View File

@ -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 */

78
security/integrity/ima/ima_main.c
View File

@ -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