On Fri, Oct 18, 2024 at 12:00:22PM +0100, Lorenzo Stoakes wrote:
> + Liam, Jann
>
> On Fri, Oct 18, 2024 at 01:49:06PM +0300, Kirill A. Shutemov wrote:
> > 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);
>
> Accessing VMA fields without any kind of lock is... very much not advised.
>
> I'm guessing you meant to say:
>
> ret = security_mmap_file(file, prot, flags);
>
> Here? :)
Sure. My bad.
Patch with all fixups:
diff --git a/mm/mmap.c b/mm/mmap.c
index dd4b35a25aeb..541787d526b6 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1646,14 +1646,41 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
if (pgoff + (size >> PAGE_SHIFT) < pgoff)
return ret;
- if (mmap_write_lock_killable(mm))
+ 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(file, prot, flags);
+ if (ret) {
+ fput(file);
+ return ret;
+ }
+
+ ret = -EINVAL;
+
+ if (mmap_write_lock_killable(mm)) {
+ fput(file);
+ return -EINTR;
+ }
+
+ vma = vma_lookup(mm, start);
+
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 +1715,11 @@ 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
