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>

1 files changed, 7 insertions, 0 deletions

diff --git a/include/linux/ima.h b/include/linux/ima.h
index aefe758f4466..9164e1534ec9 100644
--- 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;