ima: detect violations for mmaped files

This patch fixes the detection of the 'open_writers' violation for mmaped
files.

before) an 'open_writers' violation is detected if the policy contains
        a rule with the criteria: func=FILE_CHECK mask=MAY_READ

after) an 'open_writers' violation is detected if the current event
       matches one of the policy rules.

With the old behaviour, the 'open_writers' violation is not detected
in the following case:

policy:
measure func=FILE_MMAP mask=MAY_EXEC

steps:
1) open a shared library for writing
2) execute a binary that links that shared library
3) during the binary execution, modify the shared library and save
   the change

result:
the 'open_writers' violation measurement is not present in the IMA list.

Only binaries executed are protected from writes. For libraries mapped
in memory there is the flag MAP_DENYWRITE for this purpose, but according
to the output of 'man mmap', the mmap flag is ignored.

Since ima_rdwr_violation_check() is now called by process_measurement()
the information about if the inode must be measured is already provided
by ima_get_action(). Thus the unnecessary function ima_must_measure()
has been removed.

Changes in v3 (Dmitry Kasatkin):
- Violation for MMAP_CHECK function are verified since this patch
- Changed patch description a bit

Signed-off-by: Roberto Sassu <roberto.sassu@polito.it>
Signed-off-by: Dmitry Kasatkin <d.kasatkin@samsung.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>

2 files changed, 5 insertions, 9 deletions

diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
index 65c41a968cc1..86885979918c 100644
--- a/security/integrity/ima/ima_api.c
+++ b/security/integrity/ima/ima_api.c
@@ -179,11 +179,6 @@ int ima_get_action(struct inode *inode, int mask, int function)
         return ima_match_policy(inode, function, mask, flags);
 }
 
-int ima_must_measure(struct inode *inode, int mask, int function)
-{
-        return ima_match_policy(inode, function, mask, IMA_MEASURE);
-}
-
 /*
  * ima_collect_measurement - collect file measurement
  *
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 03bb52ecf490..62f59eca32d3 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -79,6 +79,7 @@ __setup("ima_hash=", hash_setup);
  */
 static void ima_rdwr_violation_check(struct file *file,
                                      struct integrity_iint_cache *iint,
+                                     int must_measure,
                                      char **pathbuf,
                                      const char **pathname)
 {
@@ -95,8 +96,7 @@ static void ima_rdwr_violation_check(struct file *file,
                                 send_tomtou = true;
                 }
         } else {
-                if ((atomic_read(&inode->i_writecount) > 0) &&
-                    ima_must_measure(inode, MAY_READ, FILE_CHECK))
+                if ((atomic_read(&inode->i_writecount) > 0) && must_measure)
                         send_writers = true;
         }
 
@@ -174,7 +174,7 @@ static int process_measurement(struct file *file, int mask, int function,
          * Included is the appraise submask.
          */
         action = ima_get_action(inode, mask, function);
-        violation_check = (function == FILE_CHECK &&
+        violation_check = ((function == FILE_CHECK || function == MMAP_CHECK) &&
                            (ima_policy_flag & IMA_MEASURE));
         if (!action && !violation_check)
                 return 0;
@@ -194,7 +194,8 @@ static int process_measurement(struct file *file, int mask, int function,
         }
 
         if (violation_check) {
-                ima_rdwr_violation_check(file, iint, &pathbuf, &pathname);
+                ima_rdwr_violation_check(file, iint, action & IMA_MEASURE,
+                                         &pathbuf, &pathname);
                 if (!action) {
                         rc = 0;
                         goto out_free;