ima: verify mprotect change is consistent with mmap policy

Files can be mmap'ed read/write and later changed to execute to circumvent
IMA's mmap appraise policy rules.  Due to locking issues (mmap semaphore
would be taken prior to i_mutex), files can not be measured or appraised at
this point.  Eliminate this integrity gap, by denying the mprotect
PROT_EXECUTE change, if an mmap appraise policy rule exists.

On mprotect change success, return 0.  On failure, return -EACESS.

Reviewed-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

diff --git a/include/linux/ima.h b/include/linux/ima.h
index aefe758..9164e15 100644 (file)
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -18,6 +18,7 @@ extern int ima_file_check(struct file *file, int mask);
 extern void ima_post_create_tmpfile(struct inode *inode);
 extern void ima_file_free(struct file *file);
 extern int ima_file_mmap(struct file *file, unsigned long prot);
+extern int ima_file_mprotect(struct vm_area_struct *vma, unsigned long prot);
 extern int ima_load_data(enum kernel_load_data_id id);
 extern int ima_read_file(struct file *file, enum kernel_read_file_id id);
 extern int ima_post_read_file(struct file *file, void *buf, loff_t size,
@@ -70,6 +71,12 @@ static inline int ima_file_mmap(struct file *file, unsigned long prot)
        return 0;
 }
 
+static inline int ima_file_mprotect(struct vm_area_struct *vma,
+                                   unsigned long prot)
+{
+       return 0;
+}
+
 static inline int ima_load_data(enum kernel_load_data_id id)
 {
        return 0;

diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index f96f151..800fb3b 100644 (file)
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -393,6 +393,57 @@ int ima_file_mmap(struct file *file, unsigned long prot)
        return 0;
 }
 
+/**
+ * ima_file_mprotect - based on policy, limit mprotect change
+ * @prot: contains the protection that will be applied by the kernel.
+ *
+ * Files can be mmap'ed read/write and later changed to execute to circumvent
+ * IMA's mmap appraisal policy rules.  Due to locking issues (mmap semaphore
+ * would be taken before i_mutex), files can not be measured or appraised at
+ * this point.  Eliminate this integrity gap by denying the mprotect
+ * PROT_EXECUTE change, if an mmap appraise policy rule exists.
+ *
+ * On mprotect change success, return 0.  On failure, return -EACESS.
+ */
+int ima_file_mprotect(struct vm_area_struct *vma, unsigned long prot)
+{
+       struct ima_template_desc *template;
+       struct file *file = vma->vm_file;
+       char filename[NAME_MAX];
+       char *pathbuf = NULL;
+       const char *pathname = NULL;
+       struct inode *inode;
+       int result = 0;
+       int action;
+       u32 secid;
+       int pcr;
+
+       /* Is mprotect making an mmap'ed file executable? */
+       if (!vma->vm_file || !(prot & PROT_EXEC) || (vma->vm_flags & VM_EXEC))
+               return 0;
+
+       security_task_getsecid(current, &secid);
+       inode = file_inode(vma->vm_file);
+       action = ima_get_action(inode, current_cred(), secid, MAY_EXEC,
+                               MMAP_CHECK, &pcr, &template, 0);
+
+       /* Is the mmap'ed file in policy? */
+       if (!(action & (IMA_MEASURE | IMA_APPRAISE_SUBMASK)))
+               return 0;
+
+       if (action & IMA_APPRAISE_SUBMASK)
+               result = -EPERM;
+
+       file = vma->vm_file;
+       pathname = ima_d_path(&file->f_path, &pathbuf, filename);
+       integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, pathname,
+                           "collect_data", "failed-mprotect", result, 0);
+       if (pathbuf)
+               __putname(pathbuf);
+
+       return result;
+}
+
 /**
  * ima_bprm_check - based on policy, collect/store measurement.
  * @bprm: contains the linux_binprm structure

diff --git a/security/security.c b/security/security.c
index 7fed24b..dd0917c 100644 (file)
--- a/security/security.c
+++ b/security/security.c
@@ -1512,7 +1512,12 @@ int security_mmap_addr(unsigned long addr)
 int security_file_mprotect(struct vm_area_struct *vma, unsigned long reqprot,
                            unsigned long prot)
 {
-       return call_int_hook(file_mprotect, 0, vma, reqprot, prot);
+       int ret;
+
+       ret = call_int_hook(file_mprotect, 0, vma, reqprot, prot);
+       if (ret)
+               return ret;
+       return ima_file_mprotect(vma, prot);
 }
 
 int security_file_lock(struct file *file, unsigned int cmd)