Re: [Linux-ima-devel] [PATCH v2 3/4] ima: check appraisal flag in the ima_file_free() hook

From: Roberto Sassu
Date: Thu Oct 02 2014 - 04:26:51 EST


On 10/01/2014 08:43 PM, Dmitry Kasatkin wrote:
ima_file_free() hook is only used by appraisal module to update hash
when file was modified. When there were no integrity checks on inode,
S_IMA flag is not set, integrity_iint_find() returns NULL and it
quits. When inode is only measured/audited but not appraised, iint
is allocated and it will cause calling ima_check_last_writer() which
unnecessarily locks i_mutex.

Currently ima_file_free() checks 'iint_initialized'. But it looks that
it is a mistake and originally 'ima_appraise' had to be used instead.
In fact usage of 'iint_initialized' is completely unnecessary because
S_IMA flag would not be set if iint was not allocated.


Hi Dmitry

sorry, I think there are two mistakes here.

First, ima_file_free() is not used by the appraisal module only
because, if a file has been written, also the IMA_MEASURED
and IMA_AUDITED flags are cleared. Your patch prevents further
measurements/audits if a file is modified.

Second, the lock of i_mutex is necessary, as it protects the
access to the fields of the 'integrity_iint_cache' structure.

My suggestion is to provide a patch that fixes the commit a756024e
of Mimi's 'next' branch. The patch should just replace the check
of 'iint_initialized' with 'ima_policy_flag'. The removal of
'iint_initialized' could be done in a separate patch.

Thanks

Roberto Sassu


This patch uses lately introduced ima_policy_flag to test if appraisal
was enabled by policy.

With this change 'iint_initialized' is no longer used anywhere. Indeed,
integrity cache is allocated with SLAB_PANIC and kernel will panic if
allocation fails during kernel initialization. So this variable is
unnecessary and thus this patch removes it.

Changes in v2:
* 'iint_initialized' removal patch merged to this patch (requested
by Mimi)

Signed-off-by: Dmitry Kasatkin <d.kasatkin@xxxxxxxxxxx>
---
security/integrity/iint.c | 3 ---
security/integrity/ima/ima_main.c | 2 +-
security/integrity/integrity.h | 3 ---
3 files changed, 1 insertion(+), 7 deletions(-)

diff --git a/security/integrity/iint.c b/security/integrity/iint.c
index a521edf..cc3eb4d 100644
--- a/security/integrity/iint.c
+++ b/security/integrity/iint.c
@@ -25,8 +25,6 @@ static struct rb_root integrity_iint_tree = RB_ROOT;
static DEFINE_RWLOCK(integrity_iint_lock);
static struct kmem_cache *iint_cache __read_mostly;

-int iint_initialized;
-
/*
* __integrity_iint_find - return the iint associated with an inode
*/
@@ -166,7 +164,6 @@ static int __init integrity_iintcache_init(void)
iint_cache =
kmem_cache_create("iint_cache", sizeof(struct integrity_iint_cache),
0, SLAB_PANIC, init_once);
- iint_initialized = 1;
return 0;
}
security_initcall(integrity_iintcache_init);
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 62f59ec..87d7df7 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -143,7 +143,7 @@ void ima_file_free(struct file *file)
struct inode *inode = file_inode(file);
struct integrity_iint_cache *iint;

- if (!iint_initialized || !S_ISREG(inode->i_mode))
+ if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode))
return;

iint = integrity_iint_find(inode);
diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h
index aafb468..f51ad65 100644
--- a/security/integrity/integrity.h
+++ b/security/integrity/integrity.h
@@ -169,6 +169,3 @@ static inline void integrity_audit_msg(int audit_msgno, struct inode *inode,
{
}
#endif
-
-/* set during initialization */
-extern int iint_initialized;


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/