On Fri, Oct 18, 2024 at 11:24:06AM +0200, Roberto Sassu wrote:

quoted

Probably it is hard, @Kirill would there be any way to safely move
security_mmap_file() out of the mmap_lock lock?

What about something like this (untested):

diff --git a/mm/mmap.c b/mm/mmap.c
index dd4b35a25aeb..03473e77d356 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c

@@ -1646,6 +1646,26 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
 	if (pgoff + (size >> PAGE_SHIFT) < pgoff)
 		return ret;
 
+	if (mmap_read_lock_killable(mm))
+		return -EINTR;
+
+	vma = vma_lookup(mm, start);
+
+	if (!vma || !(vma->vm_flags & VM_SHARED)) {
+		mmap_read_unlock(mm);
+		return -EINVAL;
+	}
+
+	file = get_file(vma->vm_file);
+
+	mmap_read_unlock(mm);
+
+	ret = security_mmap_file(vma->vm_file, prot, flags);
+	if (ret) {
+		fput(file);
+		return ret;
+	}
+

 	if (mmap_write_lock_killable(mm))
 		return -EINTR;
 

@@ -1654,6 +1674,9 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
 	if (!vma || !(vma->vm_flags & VM_SHARED))
 		goto out;
 
+	if (vma->vm_file != file)
+		goto out;
+
 	if (start + size > vma->vm_end) {
 		VMA_ITERATOR(vmi, mm, vma->vm_end);
 		struct vm_area_struct *next, *prev = vma;

@@ -1688,16 +1711,11 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
 	if (vma->vm_flags & VM_LOCKED)
 		flags |= MAP_LOCKED;
 
-	file = get_file(vma->vm_file);
-	ret = security_mmap_file(vma->vm_file, prot, flags);
-	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);
+	fput(file);
 	if (populate)
 		mm_populate(ret, populate);
 	if (!IS_ERR_VALUE(ret))

-- 
  Kiryl Shutsemau / Kirill A. Shutemov