Re: [integrity?] [lsm?] possible deadlock in process_measurement (4)

[Edward Adam Davis]

security_mmap_file() don't require protection from mm->mmap_lock, so we can
remove it when calling security_mmap_file.

#syz test

diff --git a/mm/mmap.c b/mm/mmap.c
index dd4b35a25aeb..97f5b150080b 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1689,15 +1689,24 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
 		flags |= MAP_LOCKED;
 
 	file = get_file(vma->vm_file);
+
+	mmap_write_unlock(mm);
 	ret = security_mmap_file(vma->vm_file, prot, flags);
+	if (mmap_write_lock_killable(mm)) {
+		fput(file);
+		goto out_pop;
+	}
+
 	if (ret)
 		goto out_fput;
+
 	ret = do_mmap(vma->vm_file, start, size,
 			prot, flags, 0, pgoff, &populate, NULL);
 out_fput:
 	fput(file);
 out:
 	mmap_write_unlock(mm);
+out_pop:
 	if (populate)
 		mm_populate(ret, populate);
 	if (!IS_ERR_VALUE(ret))