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

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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: Florent Revest <revest@google.com>
Reviewed-by: KP Singh <kpsingh@chromium.org>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
This commit is contained in:
Florent Revest 2020-01-13 10:42:44 +01:00 committed by Mimi Zohar
parent 5350ceb0b7
commit 6beea7afcc
2 changed files with 55 additions and 0 deletions
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6
include/linux/ima.h
View File

@ -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 */

49
security/integrity/ima/ima_main.c
View File

@ -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