IMA: use inode->i_lock to protect read and write counters

Currently IMA used the iint->mutex to protect the i_readcount and
i_writecount.  This patch uses the inode->i_lock since we are going to
start using in inode objects and that is the most appropriate lock.

Signed-off-by: Eric Paris <eparis@redhat.com>
Acked-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 24 insertions, 34 deletions

diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index f7af0110bcde..80aca3d2cb71 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -106,6 +106,7 @@ struct ima_iint_cache {
         unsigned char flags;
         u8 digest[IMA_DIGEST_SIZE];
         struct mutex mutex;     /* protects: version, flags, digest */
+        /* protected by inode->i_lock */
         unsigned int readcount; /* measured files readcount */
         unsigned int writecount;/* measured files writecount */
         struct kref refcount;   /* ima_iint_cache reference count */
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 5a1bf3df11f8..2f9b5d50424e 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -85,42 +85,12 @@ out:
         return found;
 }
 
-/* ima_read_write_check - reflect possible reading/writing errors in the PCR.
- *
- * When opening a file for read, if the file is already open for write,
- * the file could change, resulting in a file measurement error.
- *
- * Opening a file for write, if the file is already open for read, results
- * in a time of measure, time of use (ToMToU) error.
- *
- * In either case invalidate the PCR.
- */
-enum iint_pcr_error { TOMTOU, OPEN_WRITERS };
-static void ima_read_write_check(enum iint_pcr_error error,
-                                 struct ima_iint_cache *iint,
-                                 struct inode *inode,
-                                 const unsigned char *filename)
-{
-        switch (error) {
-        case TOMTOU:
-                if (iint->readcount > 0)
-                        ima_add_violation(inode, filename, "invalid_pcr",
-                                          "ToMToU");
-                break;
-        case OPEN_WRITERS:
-                if (iint->writecount > 0)
-                        ima_add_violation(inode, filename, "invalid_pcr",
-                                          "open_writers");
-                break;
-        }
-}
-
 /*
  * Update the counts given an fmode_t
  */
 static void ima_inc_counts(struct ima_iint_cache *iint, fmode_t mode)
 {
-        BUG_ON(!mutex_is_locked(&iint->mutex));
+        assert_spin_locked(&iint->inode->i_lock);
 
         if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
                 iint->readcount++;
@@ -146,6 +116,7 @@ void ima_counts_get(struct file *file)
         fmode_t mode = file->f_mode;
         struct ima_iint_cache *iint;
         int rc;
+        bool send_tomtou = false, send_writers = false;
 
         if (!iint_initialized || !S_ISREG(inode->i_mode))
                 return;
@@ -153,22 +124,35 @@ void ima_counts_get(struct file *file)
         if (!iint)
                 return;
         mutex_lock(&iint->mutex);
+        spin_lock(&inode->i_lock);
+
         if (!ima_initialized)
                 goto out;
+
         rc = ima_must_measure(iint, inode, MAY_READ, FILE_CHECK);
         if (rc < 0)
                 goto out;
 
         if (mode & FMODE_WRITE) {
-                ima_read_write_check(TOMTOU, iint, inode, dentry->d_name.name);
+                if (iint->readcount)
+                        send_tomtou = true;
                 goto out;
         }
-        ima_read_write_check(OPEN_WRITERS, iint, inode, dentry->d_name.name);
+
+        if (atomic_read(&inode->i_writecount) > 0)
+                send_writers = true;
 out:
         ima_inc_counts(iint, file->f_mode);
+        spin_unlock(&inode->i_lock);
         mutex_unlock(&iint->mutex);
-
         kref_put(&iint->refcount, iint_free);
+
+        if (send_tomtou)
+                ima_add_violation(inode, dentry->d_name.name, "invalid_pcr",
+                                  "ToMToU");
+        if (send_writers)
+                ima_add_violation(inode, dentry->d_name.name, "invalid_pcr",
+                                  "open_writers");
 }
 
 /*
@@ -181,6 +165,7 @@ static void ima_dec_counts(struct ima_iint_cache *iint, struct inode *inode,
         bool dump = false;
 
         BUG_ON(!mutex_is_locked(&iint->mutex));
+        assert_spin_locked(&inode->i_lock);
 
         if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) {
                 if (unlikely(iint->readcount == 0))
@@ -223,7 +208,11 @@ void ima_file_free(struct file *file)
                 return;
 
         mutex_lock(&iint->mutex);
+        spin_lock(&inode->i_lock);
+
         ima_dec_counts(iint, inode, file);
+
+        spin_unlock(&inode->i_lock);
         mutex_unlock(&iint->mutex);
         kref_put(&iint->refcount, iint_free);
 }