[RFC PATCH 15/30] ima: Add a reader counter to the integrity inode data
krzysztof.struczynski at huawei.com
krzysztof.struczynski at huawei.com
Tue Aug 18 15:42:15 UTC 2020
From: Krzysztof Struczynski <krzysztof.struczynski at huawei.com>
To detect ToMToU violations reader counter of the given inode is
checked. This is not enough, because the reader may exist in a
different ima namespace. Per inode reader counter tracks readers in all
ima namespaces, whereas the per namespace counter is necessary to avoid
false positives.
Add a new reader counter to the integrity inode cache entry.
Signed-off-by: Krzysztof Struczynski <krzysztof.struczynski at huawei.com>
---
security/integrity/ima/ima_main.c | 71 ++++++++++++++++++++++---------
security/integrity/integrity.h | 18 ++++++++
2 files changed, 70 insertions(+), 19 deletions(-)
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index b933c7e6c8e1..6555cdf6b65e 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -28,6 +28,11 @@
#include "ima.h"
+struct ima_file_data {
+ struct ima_namespace *ima_ns;
+ bool is_readcount;
+};
+
int ima_hash_algo = HASH_ALGO_SHA1;
static int hash_setup_done;
@@ -116,8 +121,8 @@ static void ima_rdwr_violation_check(struct file *file,
iint = integrity_iint_rb_find(ima_ns->iint_tree,
inode);
/* IMA_MEASURE is set from reader side */
- if (iint && test_bit(IMA_MUST_MEASURE,
- &iint->atomic_flags))
+ if (iint && atomic_read(&iint->readcount) &&
+ test_bit(IMA_MUST_MEASURE, &iint->atomic_flags))
send_tomtou = true;
}
} else {
@@ -171,7 +176,7 @@ static void ima_check_last_writer(struct integrity_iint_cache *iint,
{
fmode_t mode = file->f_mode;
bool update;
- struct ima_namespace *ima_ns = (struct ima_namespace *)file->f_ima;
+ struct ima_file_data *f_data = (struct ima_file_data *)file->f_ima;
if (!(mode & FMODE_WRITE))
return;
@@ -186,7 +191,7 @@ static void ima_check_last_writer(struct integrity_iint_cache *iint,
iint->flags &= ~(IMA_DONE_MASK | IMA_NEW_FILE);
iint->measured_pcrs = 0;
- ima_check_active_ns(ima_ns, inode);
+ ima_check_active_ns(f_data->ima_ns, inode);
if (update)
ima_update_xattr(iint, file);
@@ -207,8 +212,18 @@ static void ima_check_last_writer(struct integrity_iint_cache *iint,
*/
int ima_file_alloc(struct file *file)
{
- file->f_ima = get_current_ns();
- get_ima_ns((struct ima_namespace *)file->f_ima);
+ struct ima_file_data *f_data;
+
+ f_data = kmalloc(sizeof(struct ima_file_data), GFP_KERNEL);
+ if (!f_data)
+ return -ENOMEM;
+
+ f_data->ima_ns = get_current_ns();
+ f_data->is_readcount = false;
+ get_ima_ns(f_data->ima_ns);
+
+ file->f_ima = f_data;
+
return 0;
}
@@ -222,27 +237,33 @@ void ima_file_free(struct file *file)
{
struct inode *inode = file_inode(file);
struct integrity_iint_cache *iint;
- struct ima_namespace *ima_ns = (struct ima_namespace *)file->f_ima;
+ struct ima_file_data *f_data = (struct ima_file_data *)file->f_ima;
if (unlikely(!(file->f_mode & FMODE_OPENED)))
goto out;
- if (!ima_ns->policy_data->ima_policy_flag || !S_ISREG(inode->i_mode))
+ if (!f_data->ima_ns->policy_data->ima_policy_flag ||
+ !S_ISREG(inode->i_mode))
goto out;
- iint = integrity_iint_rb_find(ima_ns->iint_tree, inode);
+ iint = integrity_iint_rb_find(f_data->ima_ns->iint_tree, inode);
if (!iint)
goto out;
ima_check_last_writer(iint, inode, file);
+
+ if (f_data->is_readcount)
+ iint_readcount_dec(iint);
out:
- put_ima_ns(ima_ns);
+ put_ima_ns(f_data->ima_ns);
+ kfree(f_data);
}
static int process_ns_measurement(struct file *file, const struct cred *cred,
u32 secid, char *buf, loff_t size, int mask,
enum ima_hooks func,
- struct ima_namespace *ima_ns)
+ struct ima_namespace *ima_ns,
+ bool readcount_open)
{
struct inode *inode = file_inode(file);
struct integrity_iint_cache *iint = NULL;
@@ -262,6 +283,12 @@ static int process_ns_measurement(struct file *file, const struct cred *cred,
if (!ima_ns->policy_data->ima_policy_flag)
return 0;
+ if (ima_ns != current_ima_ns) {
+ iint = integrity_iint_rb_find(ima_ns->iint_tree, inode);
+ if (!iint)
+ return 0;
+ }
+
/* Return an IMA_MEASURE, IMA_APPRAISE, IMA_AUDIT action
* bitmask based on the appraise/audit/measurement policy.
* Included is the appraise submask.
@@ -282,12 +309,18 @@ static int process_ns_measurement(struct file *file, const struct cred *cred,
inode_lock(inode);
- if (action) {
+ if (action && !iint) {
iint = integrity_inode_rb_get(ima_ns->iint_tree, inode);
if (!iint)
rc = -ENOMEM;
}
+ if ((ima_ns == current_ima_ns) && iint && readcount_open &&
+ ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)) {
+ iint_readcount_inc(iint);
+ ((struct ima_file_data *)file->f_ima)->is_readcount = true;
+ }
+
if (!rc && violation_check)
ima_rdwr_violation_check(file, iint, action & IMA_MEASURE,
&pathbuf, &pathname, filename, ima_ns);
@@ -429,7 +462,7 @@ static int process_ns_measurement(struct file *file, const struct cred *cred,
static int process_measurement(struct file *file, const struct cred *cred,
u32 secid, char *buf, loff_t size, int mask,
- enum ima_hooks func)
+ enum ima_hooks func, bool readcount_open)
{
int ret;
struct ima_namespace *ima_ns;
@@ -444,7 +477,7 @@ static int process_measurement(struct file *file, const struct cred *cred,
continue;
ret = process_ns_measurement(file, cred, secid, buf, size, mask,
- func, ima_ns);
+ func, ima_ns, readcount_open);
if (ret != 0)
break;
}
@@ -471,7 +504,7 @@ int ima_file_mmap(struct file *file, unsigned long prot)
if (file && (prot & PROT_EXEC)) {
security_task_getsecid(current, &secid);
return process_measurement(file, current_cred(), secid, NULL,
- 0, MAY_EXEC, MMAP_CHECK);
+ 0, MAY_EXEC, MMAP_CHECK, true);
}
return 0;
@@ -551,13 +584,13 @@ int ima_bprm_check(struct linux_binprm *bprm)
security_task_getsecid(current, &secid);
ret = process_measurement(bprm->file, current_cred(), secid, NULL, 0,
- MAY_EXEC, BPRM_CHECK);
+ MAY_EXEC, BPRM_CHECK, false);
if (ret)
return ret;
security_cred_getsecid(bprm->cred, &secid);
return process_measurement(bprm->file, bprm->cred, secid, NULL, 0,
- MAY_EXEC, CREDS_CHECK);
+ MAY_EXEC, CREDS_CHECK, false);
}
/**
@@ -577,7 +610,7 @@ int ima_file_check(struct file *file, int mask)
security_task_getsecid(current, &secid);
return process_measurement(file, current_cred(), secid, NULL, 0,
mask & (MAY_READ | MAY_WRITE | MAY_EXEC |
- MAY_APPEND), FILE_CHECK);
+ MAY_APPEND), FILE_CHECK, true);
}
EXPORT_SYMBOL_GPL(ima_file_check);
@@ -779,7 +812,7 @@ int ima_post_read_file(struct file *file, void *buf, loff_t size,
func = read_idmap[read_id] ?: FILE_CHECK;
security_task_getsecid(current, &secid);
return process_measurement(file, current_cred(), secid, buf, size,
- MAY_READ, func);
+ MAY_READ, func, false);
}
/**
diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h
index 721d1850e4f9..c2981a98547e 100644
--- a/security/integrity/integrity.h
+++ b/security/integrity/integrity.h
@@ -17,6 +17,7 @@
#include <crypto/sha.h>
#include <linux/key.h>
#include <linux/audit.h>
+#include <linux/atomic.h>
/* iint action cache flags */
#define IMA_MEASURE 0x00000001
@@ -138,6 +139,9 @@ struct integrity_iint_cache {
enum integrity_status ima_creds_status:4;
enum integrity_status evm_status:4;
struct ima_digest_data *ima_hash;
+ atomic_t readcount; /* Reader counter, incremented only in FILE_CHECK or
+ * MMAP_CHECK hooks, used for ima violation check.
+ */
};
struct integrity_iint_tree {
@@ -294,3 +298,17 @@ static inline void __init add_to_platform_keyring(const char *source,
{
}
#endif
+
+#ifdef CONFIG_IMA
+static inline void iint_readcount_inc(struct integrity_iint_cache *iint)
+{
+ atomic_inc(&iint->readcount);
+}
+static inline void iint_readcount_dec(struct integrity_iint_cache *iint)
+{
+ if (WARN_ON(!atomic_read(&iint->readcount)))
+ return;
+
+ atomic_dec(&iint->readcount);
+}
+#endif
--
2.20.1
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