Re: [PATCH 1/3] ima: Remove inode lock

[Kirill A. Shutemov]

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