integrity: Fix possible multiple allocation in integrity_inode_get()

When integrity_inode_get() is querying and inserting the cache, there
is a conditional race in the concurrent environment.

The race condition is the result of not properly implementing
"double-checked locking". In this case, it first checks to see if the
iint cache record exists before taking the lock, but doesn't check
again after taking the integrity_iint_lock.

Fixes: bf2276d10ce5 ("ima: allocating iint improvements")
Signed-off-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
Cc: Dmitry Kasatkin <dmitry.kasatkin@gmail.com>
Cc: <stable@vger.kernel.org> # v3.10+
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

diff --git a/security/integrity/iint.c b/security/integrity/iint.c
index c73858e..a462df8 100644 (file)
--- a/security/integrity/iint.c
+++ b/security/integrity/iint.c
@@ -43,12 +43,10 @@ static struct integrity_iint_cache *__integrity_iint_find(struct inode *inode)
                else if (inode > iint->inode)
                        n = n->rb_right;
                else
-                       break;
+                       return iint;
        }
-       if (!n)
-               return NULL;
 
-       return iint;
+       return NULL;
 }
 
 /*
@@ -113,10 +111,15 @@ struct integrity_iint_cache *integrity_inode_get(struct inode *inode)
                parent = *p;
                test_iint = rb_entry(parent, struct integrity_iint_cache,
                                     rb_node);
-               if (inode < test_iint->inode)
+               if (inode < test_iint->inode) {
                        p = &(*p)->rb_left;
-               else
+               } else if (inode > test_iint->inode) {
                        p = &(*p)->rb_right;
+               } else {
+                       write_unlock(&integrity_iint_lock);
+                       kmem_cache_free(iint_cache, iint);
+                       return test_iint;
+               }
        }
 
        iint->inode = inode;